Labelling Strategies for the Sensitive Detection of Analytes

ABSTRACT

The present invention relates to methods and reagents for detecting analytes, e.g. nucleic acids. The new methods and reagents allow a simple and sensitive detection even in complex biological samples.

This application is a continuation of U.S. application Ser. No.11/913,156, filed Dec. 23, 2008, which application is a National Stageapplication of International Application No. PCT/EP2006/004017, filedApr. 28, 2006, which claims the benefit of U.S. Provisional ApplicationNo. 60/676,785, filed May 2, 2005; and U.S. Provisional Application No.60/750,100, filed Dec. 14, 2005 the entire contents of which is herebyincorporated herein by reference. International Application No.PCT/EP2006/004017 also claims the benefit under 35 U.S.C. §119 ofEuropean Patent Application No. EP 05009618.9, filed May 2, 2005; andEuropean Patent Application No. EP 05027370.5, filed Dec. 14, 2005.

Submitted herewith is a Sequence Listing in computer readable format(CRF) which corresponds to the paper Sequence Listing that wasoriginally submitted on Apr. 27, 2009 in U.S. application Ser. No.11/913,156.

DESCRIPTION

The present invention relates to methods and reagents for detectinganalytes, e.g. nucleic acids. The new methods and reagents allow asimple and sensitive detection even in complex biological samples.

BACKGROUND OF THE INVENTION

The rapid analysis of genetic material for specific target sequences,e.g. for the presence of single nucleotide polymorphisms, the presenceof a certain gene; e.g. a resistance gene, or of mRNA requires easy touse, efficient and reliable new tools. The major problem is the need todetect the DNA or RNA of interest directly in small biological samplessuch as patient blood or plants. These provide the analyte only inminute amounts. In order to reach the required sensitivity anamplification step is usually required wherein either the nucleic acidanalyte is amplified prior to analysis or a detection method is used inwhich the minute detection signal, directly obtained from the DNA/RNAanalyte, is amplified.

Methods for the amplification of the nucleic acid analyte include PCRand other nucleic acid amplification protocols. PCR amplification hasthe major advantage that, within a pool of different DNA strandsobtained from the biological material, only the DNA sequence of interestis amplified. This is the basis for the reliable analysis of singlegenes in complex biological samples. PCR amplification, however,requires complex process steps which, in some cases, are tooinconvenient and expensive. Amplification of the detection signal may beachieved by binding an enzyme such a horse radish peroxidase to theanalyte, which converts a given substrate continuously into a coloredproduct.

DNA metallization is another way to amplify the detection signal. Asingle metallic particle attached to DNA/RNA (the nucleus) catalyzes thedeposition of ever more metal, which catalyzes further metal deposition[1-9]. The signal induced by metal deposition grows accordingly in anexponential manner. The metal deposition can be detected eitherelectrically, if the analyte is placed within two electrodes, oroptically (e.g. with the eye) because the deposited metal gives rise toa black spot e.g. on paper, in the gel, or in the test tube. Inprinciple, metal deposition is the most sensitive detection methodbecause a small metal cluster (nucleus) is sufficient to start thereaction. In practice, however, the sensitivity of the method is limitedby unspecific metal nucleation e.g. through impurities in close spatialvicinity to the analyte for example, on the electrodes, in the gel, oron the paper holding the analyte. In fact unspecific metal deposition isthe major reason why silver staining of DNA is not routinely used inoligonucleotide analytics. Silver staining is further complicated by thefact that DNA is unable to build the initiation nucleus itself. Itrequires prior modification. The method of choice today is the reactionof DNA with glutaraldehyde which covalently attaches to the DNA bysequence-unspecific binding to primary amine groups on nucleobase [7].This adduct, if treated with a silver salt, reduces the Ag⁺ of the saltto atomic silver which, while bound to the DNA, functions as therequired nucleus. Further treatment of the nucleated DNA with silversalts and reducing agents initiates the exponential metal deposition.Another possibility is to exchange the counterions on the DNA strand byAg⁺, which is subsequently reduced to give Ag⁰ nucleation sites. Themajor disadvantage is that the glutaraldehyde also reacts withimpurities or other chemical species close to the analyte, which againinduces unspecific silver deposition.

Metal clusters such as Au, Pd particles or Pt-complexes attached to DNAalso function as nucleation sites for further metal deposition up to theconstruction of conducting wires [1-9]. Here the clusters are attachedto reactive groups which form a covalent bond with DNA or to units thatjust intercalate or bind otherwise to DNA/RNA. All these methods labelthe entire DNA in a biological sample and therefore do not allowsequence-specific marking and hence sequence-specific analysis of atarget DNA such as a single gene in a complex biological sample.

The preparation of labelled DNA domains by a telomerase-mediatedincorporation of amine-modified nucleoside triphosphates into aprimer-initiated modified telomer repeat is described in [8]. Theamine-containing telomers are functionalized with activated goldnanoparticle N-succinimidyl esters to yield gold nanoparticle DNAstrands. Enlargement of these nanoparticle sites by further metaldeposition along the DNA indeed yields rapid growth of the metalclusters up to the construction of DNA templated molecular nanowires.However, the efficiency of amine-modified triphosphate incorporationinto the growing telomer end is low and requires triphosphate dopingwhich results in a distribution of nucleation sites. Thus, the proceduredoes not allow sequence-specific labelling.

Site-specific labelling of DNA has also recently been attempted via acomplex lithographic method [4]. According to this method, a partialprotection of DNA molecules is effected by binding of RecA. Theunprotected DNA sequences are then treated with glutaraldehyde whichmarks these sequences for metallization. Site-specific reduction ofsilver ions by the DNA-bound aldehyde functions results in wireformation along these regions. A sequence-specific labelling of nucleicacid molecules in a complex biological sample is not possible, however.

Although these documents demonstrate the interest in new labellingstrategies of DNA, the complicated processes involved in order toachieve marking prevents these systems from being used for any realapplication. In particular, these methods are unable to selectivelylabel DNA or RNA sequences of interest directly in a crude biologicalsample.

Thus it was an object of the present invention to provide novel methodsand reagents which allow a simple, efficient and specific detection ofanalytes, particularly of nucleic acids in complex biological samples.

SUMMARY OF THE INVENTION

A first aspect of the present invention relates to methods and reagentkits for detecting an analyte, e.g. an analyte, e.g. a nucleic acid in asample, wherein an association product of the analyte to be detectedwith a novel aldehyde-functionalized compound is formed, which allowssequence-specific detection by forming marker groups, e.g. metaldepositions around aldehyde groups in said association product.

More particularly, an embodiment of this aspect relates to a method fordetecting an analyte in a sample comprising the steps:

-   -   1 (i) providing a sample;    -   2 (ii) contacting the sample with a functionalized compound        comprising at least one functional group selected from an        aldehyde group, a protected aldehyde group, an aldehyde        precursor group or a handle group for introducing an aldehyde        group, a protected aldehyde group or an aldehyde precursor        group, under conditions wherein said compound forms an        association product with the analyte to be detected;    -   3 (iii) if necessary, reacting the handle group with a reaction        partner, comprising an aldehyde group, a protected aldehyde        group or an aldehyde precursor group,    -   4 (iv) if necessary, converting protected aldehyde groups and        aldehyde precursor groups to aldehyde groups,    -   5 (v) contacting said association product having aldehyde groups        with a marker reagent under conditions wherein marker groups are        formed around aldehyde groups in said association product, and    -   6 (vi) detecting said marker groups.

A further embodiment of this first aspect relates to a reagent kit fordetecting an analyte in a sample, comprising:

-   -   1 (a) a functionalized compound comprising a functional group        selected from an aldehyde group, a protected aldehyde group or        an aldehyde precursor group, or a handle group for introducing        an aldehyde group, a protected aldehyde group or an aldehyde        precursor group,    -   2 (b) optionally a reaction partner for the handle group        comprising an aldehyde group, a protected aldehyde group or an        aldehyde precursor group,    -   3 (c) optionally an aldehyde-forming reagent capable of        converting protected aldehyde groups and aldehyde precursor        groups to aldehyde groups, and    -   4 (d) a marker reagent.

Still a further embodiment of this first aspect relates to a compound offormula (I):

31 A-S—N

wherein A is a functional group selected from an aldehyde group, aprotected aldehyde group or an aldehyde precursor group,S is a spacer or a bond, preferably a covalent bond, andN is a nucleic acid or nucleic acid analogue building block such as anucleosidic or nucleotidic compound.

In a second aspect the present invention relates to methods and reagentkits for detecting an analyte, e.g. a nucleic acid in a sample involvingthe use of a Click-functionalized compound which forms an associationproduct with the analyte to be detected. The sequence-specificintroduction of marker groups is effected by reacting theClick-functionalized compound with, a suitable reaction partnercomprising marker groups or marker precursor groups.

An embodiment of this second aspect relates to a method for detecting ananalyte in a sample comprising the steps:

-   -   1 (i) providing a sample;    -   2 (ii) contacting the sample with a functionalized compound        comprising at least one functional group which is a first        reaction partner for a Click reaction under conditions wherein        said compound forms an association product with the analyte to        be detected,    -   3 (iii) contacting the association product with a second        reaction partner for a Click reaction under conditions wherein a        Click reaction between the first and second reaction partner        occurs, wherein the second reaction partner further comprises a        marker group or a marker precursor group,    -   4 (iv) if necessary, converting marker precursor groups to        marker groups, and    -   5 (v) detecting said marker groups.

A further embodiment of this second aspect relates to a reagent kit fordetecting an analyte in a sample, comprising:

-   -   1 (a) a functionalized compound comprising at least one        functional group which is a first reaction partner for a Click        reaction,    -   2 (b) a second reaction partner for a Click reaction, wherein        the second reaction partner further comprises a marker group or        a marker precursor group, and    -   3 (c) optionally a marker forming reagent capable of converting        marker precursor groups to marker groups.

Still a further embodiment of this second aspect relates to a compoundof the formula (II):

C—S—N

wherein C is a functional group which is a first reaction partner for aClick reaction,S is a spacer or a bond, preferably a covalent bond andN is a nucleic acid or nucleic acid analogue building block such as anucleosidic or nucleotidic compound.

In a third aspect the present invention relates to methods and reagentkits for detecting an analyte, e.g. a nucleic acid in a sample involvingthe use of a photosensitizer compound which forms an association productwith the analyte to be detected. Preferably, photosensitizer groups aresequence-specifically introduced into a nucleic acid. The presence ofphotosensitizer groups is detected by irradiating the labelledassociation product in contact with a photosensitive medium, wherein thepresence of photosensitizer groups selectively causes a site-specificformation of marker groups in the marker medium.

An embodiment of this third aspect relates to a method for detecting ananalyte in a sample by forming an association product of the analyte anda functionalized compound comprising photosensitizer groups andeffecting an energy transfer, particularly a transfer of radiationenergy from the photosensitizer groups to a photosensitive mediumwherein the energy transfer causes selective formation of marker groupsin the photosensitive medium.

A further embodiment of this third aspect relates to a method fordetecting an analyte in a sample comprising the steps:

-   -   i providing a sample;    -   ii contacting the sample with a functionalized compound        comprising at least one functional group selected from a        photosensitizer group or a handle group for introducing a        photosensitizer group under conditions wherein said compound        forms an association product with the analyte to be detected;    -   iii if necessary, reacting the handle group with a reaction        partner comprising a photosensitizer group;    -   iv irradiating said association product in contact with a        photosensitive medium under conditions wherein marker groups are        formed in said photosensitive medium in the presence of        photosensitizer groups in said association product, and    -   v detecting said marker groups.

Still a further embodiment of this third aspect relates to a reagent kitfor detecting an analyte in a sample, comprising:

-   -   a a functionalized compound comprising at least one functional        group selected from a photosensitizer group or a handle group        for introducing a photosensitizer group;    -   b optionally a reaction partner for the handle group comprising        a photosensitizer group, and;    -   c a photosensitive medium which forms marker groups upon        irradiation in the presence of photosensitizer groups.

The present invention allows a highly sensitive detection of an analyte,e.g. nucleic acids or nucleic acid binding proteins, in biologicalsamples, e.g. clinical samples, environmental samples or agriculturalsamples. Preferred applications include, but are not limited to, thedetection of genetic variabilities, e.g. single nucleotide polymorphisms(SNPs), pesticide or medicament resistances, tolerances or intolerances,genotyping, e.g. the detection of species or strains of organisms, thedetection of genetically modified organisms or strains, or the detectionof pathogens or pests, and the diagnosis of diseases, e.g. geneticdiseases, allergic diseases, autoimmune diseases or infectious diseases.A further preferred application is the detection of nucleic acids insamples for brand protection, wherein products such agriculturalproducts, food products, or goods of value and/or packaging of theseproducts are encoded with product-specific information, e.g. but notlimited to production site, date production, distributor etc., andwherein this information is detected with the methods as describedabove.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention provides methods and reagents that allow specificlabelling of analytes with marker groups, e.g. with reactive aldehydegroups in a complex sample. In a preferred embodiment, metal deposition,e.g. silver deposition, can be effected specifically on the aldehydegroups associated with the nucleic acid to be detected. In a furtherpreferred embodiment, metal deposition, e.g. silver deposition can beeffected specifically by energy transfer from photosensitizing groupsinto a photosensitive medium, e.g. photographic paper. Due to thespecific labelling procedure, the background is strongly reduced andhigher sensitivities and reliabilities are obtained.

The present invention comprises the detection of an analyte. Thedetection may be a qualitative detection, e.g. the determination of thepresence or absence of an analyte, e.g. a specific nucleic acid sequencein the sample to be analysed. The invention, however, also allowsquantitative detection of an analyte, e.g. a nucleic acid sequence, inthe sample to be analysed. Qualitative and/or quantitative detection maycomprise the determination of labelling groups according to methodsknown in the art.

The analyte to be detected is preferably selected from nucleic acids andnucleoside-, nucleotide- or nucleic acid-binding molecules, e.g.nucleoside-, nucleotide- or nucleic acid-binding proteins. Morepreferably, the analyte is a nucleic acid, e.g. any type of nucleic acidwhich can be detected according to known techniques, particularlyhybridization techniques. For example, nucleic acid analytes may beselected from DNA, e.g. double-stranded or single-stranded DNA, RNA, orDNA-RNA hybrids. Particular examples of nucleic acid analytes aregenomic DNA, mRNA or products derived therefrom, e.g. cDNA.

The method of the invention can be carried out according to any knowntest format which is suitable for the detection of analytes,particularly nucleic acid analytes in a sample. For example, the methodmay involve the detection of analytes immobilized on solid surfaces suchas membranes, e.g. in Southern or Northern blots, chips, arrays orparticles such as beads. Further, the detection can be carried out ingels, e.g. after electrophoretic separation of the sample in gels, e.g.agarose or polyacrylamide gels. The method may involve the detection ofsingle analytes or the parallel detection of a plurality of analytes,e.g. in a chip or microarray format.

In a preferred embodiment the detection involves irradiating aphotosensitive medium in the presence of a sample containing anassociation product indicative for an analyte wherein the associationproduct comprises photosensitizer groups capable of effecting an energytransfer to the photosensitive medium wherein marker groups are formedin the medium.

The sample may be any sample which may contain the analyte to bedetected. For example, the sample may be a biological sample, such as anagricultural sample, e.g. a sample comprising plant material and/ormaterial associated with the site where plants grow, plant materials arestored or processed. On the other hand, the sample may also be aclinical sample, such as a tissue sample or a body fluid sample such asblood, serum, plasma, etc, particularly of human origin. Further typesof samples include, but are not limited to, environmental samples, soilsamples, food samples, forensic samples or samples from valuable goodswhich are tested for brand protection.

Due to its high sensitivity, the method of the present invention issuitable for detecting analytes directly without amplification.According to the invention, even minute amounts of analytes, e.g. ofnucleic acids, e.g. 0.1 ng or lower, preferably 0.01 ng or lower, morepreferably 1 pg or lower, still more preferably 0.1 pg or lower, evenmore preferably 0.01 pg or lower and most preferably 0.001 pg or lowermay be determined even without amplification. An especially highsensitivity may be obtained by incorporating multiple modifiednucleotides into a nucleic acid molecule by using unprotected aldehydegroups and/or by using optimized staining techniques. For example, thedetection of an analyte, e.g. a gene, in a biological sample, might beperformed by a combination of Southern blotting and the inventivemethod. It should be noted, however, that the method of the presentinvention also allows the detection of nucleic acids combined with anamplification step, which may be carried out according to knownprotocols such as PCR or modifications thereof, such as asymmetric PCR,real-time PCR, reverse transcription PCR, etc, or other amplificationprotocols such as LCR.

In a preferred embodiment of the invention, a sequence-specificdetection of the analyte is carried out, wherein for example a nucleicacid having a specific sequence is distinguished from other nucleic acidsequences in the sample or a polypeptide capable of binding a specificnucleic acid sequence is distinguished from other polypeptides in thesample. Such a sequence-specific detection preferably comprises asequence-specific hybridization reaction by which the nucleic acidsequence to be detected is associated with a compound carrying a markergroup or a marker precursor group. It should be noted, however, that thepresent invention also allows sequence-unspecific detection of nucleicacids, e.g. detection of any nucleic acids present in a sample.

In order to identify the analyte to be detected, the sample may becontacted with an aldehyde-functionalized, Click-functionalized orphotosensitizer-functionalized compound under conditions wherein anassociation product with the analyte, e.g. a nucleic acid is formed. Analdehyde-functionalized compound comprises a functional group which maybe an aldehyde group, a protected aldehyde group, an aldehyde precursorgroup, i.e. a group which may be converted to an aldehyde group withouta significant detrimental effect on the detection procedure or a handlegroup for introducing an aldehyde group, a protected aldehyde group oran aldehyde precursor group.

The functionalized compound may comprise a single functional group or aplurality of functional groups. For example, a functionalized compoundmay be coupled to a dendrimeric moiety comprising a plurality, e.g. 2,3, 4, 5, 6, 7, 8 or more functional groups as indicated above.Dendrimeric moieties may be synthesized by known techniques. Preferablydendrimeric moieties are synthesized via Click reactions, e.g. asdescribed in Example 5.

The functional group is attached to a compound which is capable offorming an association product with the analyte. The compound may be anucleosidic or nucleotidic compound, e.g. a nucleoside or nucleosideanalogue or a nucleotide or nucleotide analogue or an oligomer orpolymer comprising at least one functionalized compound, e.g. a nucleicacid or nucleic acid analogue. A nucleosidic or nucleotidic compound isa nucleoside or nucleotide analogue or a nucleotide or nucleotideanalogue capable of being incorporated into nucleic acids or nucleicacid analogues, e.g. by chemical or enzymatic methods. The resultingnucleic acid or nucleic analogue should be capable of formingassociation products, e.g. nucleic acid hybrids, with the analyte.Preferably, the compound comprises a base moiety, e.g. a nucleobase oranother heterocyclic base moiety capable of forming base pairs with anucleobase, and a backbone moiety, e.g. comprising a sugar moiety andoptionally a phosphate moiety in nucleosides or nucleotides or adifferent backbone moiety in nucleoside or nucleotide analogues.

Preferred examples of functional nucleosidic compounds, wherein thenucleobase is 7-dN-G, C, 7-dN-A or T, and R is a functional group areshown in FIG. 1.

Preferably, the functional group is attached to a base moiety, e.g. to anucleobase. The functional group, however, may also be attached to abackbone moiety, e.g. a sugar group, a phosphate group or, in the caseof nucleoside or nucleotide analogues, a modified sugar group, amodified phosphate group or peptide backbone moiety, etc. Preferably,the functional group is covalently attached to the compound via a directbond or via a spacer. If the attachment is effected via a spacer, thefunctional group may be linked to an aliphatic or cycloaliphatic group,an aromatic or heteroaromatic group, an alkene group and/or an alkynegroup. More preferably, the functional group may be linked to aromaticor heteroaromatic groups or to alkyne groups. Especially preferredaldehyde groups include aromatic and aliphatic aldehyde groups such asbenzaldehyde, or aldehyde groups in aldoses such as trioses, tetroses,pentoses or hexoses like glucose or mannose.

The functional group may be a free aldehyde group. The functional groupmay also be a protected aldehyde group, i.e. group which may beconverted under the assay conditions to an aldehyde group. A preferredprotected aldehyde group is an acetal or hemiacetal group which can beconverted into a free aldehyde group by treatment with acids, e.g.organic or inorganic acids. Preferred examples of acetal or hemiacetalgroups are acetal groups formed with a polyalcohol such as propane diolor ethylene glycol, or hemiacetal groups in a sugar or in asugar-related compound such as an aldose sugar, e.g. glucose orgalactose. Further examples of protected aldehyde groups are iminogroups (e.g. ═NH groups), which give aldehyde groups upon treatment withacids, thioacetal or dithioacetal groups (e.g. C(SR)₂ groups wherein Rmay be an alkyl radical) which give aldehyde groups upon treatment withmercury salts, oxime groups (e.g. ═NOH groups), which give aldehydegroups upon treatment with acids, hydrazone groups (e.g. ═N—NHR groupswherein R may be an alkyl radical) which give aldehyde groups upontreatment with acids and imidazolone or imidazolidine groups orbenzothiazole or dihydrobenzothiazole groups which give aldehydes uponhydrolysis, e.g. with acid. Specific examples of functionalizedcompounds comprising free or protected aldehyde groups and methods forpreparing such compounds are shown in FIGS. 2, 3 a, 3 c, 7, 8, 9 d, and9 e.

The functional group may also be an aldehyde precursor group, i.e. agroup which may be converted to an aldehyde group without a significantdetrimental effect on the nucleic acid detection procedure. Preferredaldehyde precursor groups may be selected from carboxylic acids andcarboxylic acid derivatives including nitriles which give aldehydes uponreduction and primary alcohols which give aldehydes upon oxidation.

In a different embodiment, the functional group may be a photosensitizergroup, i.e. a group which is capable of effecting an energy transfer,e.g. a transfer of light energy, to a photosensitive medium, i.e. aphotographic medium such as photographic paper. The photosensitizergroups may be selected from known fluorescent and/or dye labellinggroups such as cyanine-based indoline groups, quinoline groups, forexample commercially available fluorescent groups such as Cy5 or Cy5.5.Specific examples of photosensitizer groups are shown in FIG. 22.

The functional group may also be a handle group, i.e. a group forintroducing an aldehyde group, a protected aldehyde group or an aldehydeprecursor group or for introducing a photosensitizer group by reactionwith a suitable reaction partner, i.e. a compound comprising one of theabove groups. In a preferred embodiment, the handle groups are selectedfrom Click functionalized groups: i.e. groups which may react with asuitable reaction partner in a cycloaddition reaction wherein a cyclic,e.g. heterocyclic linkage between the click functional group and thereaction partner is formed, and wherein the reaction partner comprisesan aldehyde or a protected aldehyde group or a photosensitizer group. Anespecially preferred example of such a Click reaction is a (3+2)cycloaddition between azide and alkyne groups which results in theformation of 1,2,3-triazole rings. Thus, aldehyde groups, may begenerated by performing a Click reaction of an azide or alkyne handlegroup and a corresponding reaction partner, i.e. a reaction partnercomprising the complementary alkyne or azide group and additionally analdehyde, a protected aldehyde group or an aldehyde precursor. In afurther embodiment of the invention, the reaction partner of theClick-functionalization, however, may also contain different marker ormarker precursor groups such as fluorescence marker groups orphotosensitizer groups.

An especially preferred embodiment of the Click reaction comprises acopper catalyzed (3+2) cycloaddition between an azide and an alkynegroup. The irreversible formation of 1,2,3-triazoles as a result of theazide/alkyne cycloaddition is orthogonal, the required chemical groupsare small (incorporation with minimal disruption of the biomolecule'senvironment) and selective due to the lack of azides and alkynes foundin nature.

wherein R₁ and R₂ are organic radicals.

Specific examples of Click-functionalized compounds and methods forpreparing such compounds are shown in FIGS. 3 b, 9 a-c and 10. Specificexamples of reaction partners for Click-functionalized compounds areshown in FIGS. 11 and 12.

The functional group, e.g. an aldehyde-functionalized group or aClick-functionalized group or a photosensitizer-functionalized group ispreferably attached to a nucleobase which may be selected from naturallyoccurring and non-naturally occurring purine and pyrimidine bases.Preferably, the nucleobases are selected from cytidine, uracil, thymine,adenine, guanine, 7-deazaadenine, 7-deazaguanine, inosine and xanthine.The functional group is preferably attached to position 5 or 6, morepreferably to position 5, of a pyrimidine nucleobase or to position 7 or8, more preferably to position 7 of a purine nucleobase, particularly ifan enzymatic incorporation into a nucleic acid is desired.

The functional group may be covalently attached to the compound, e.g.via a direct bond or a spacer, e.g. a spacer having a chain length up to20 atoms. The spacer may be a flexible spacer, e.g. an alkylene-basedspacer, optionally containing heteroatoms such as O, S, and/or N or anat least partially rigid spacer, e.g. a spacer which comprises at leastone rigid group selected from alkene groups, alkyne groups, cyclicgroups, particularly aromatic or heteroaromatic groups, but alsocycloaliphatic groups and combinations thereof. If the functionalizationcompound comprises a Click-functionalization group which is the firstreaction partner for a Click-reaction and subsequently reacted with asecond reaction partner for a Click-reaction, an attachment of thefunctional group via a direct bond, a flexible spacer or an partiallyrigid spacer is preferred wherein the flexible spacer could for examplehave a chain length up to 6 atoms, more particularly up to 4 atoms, andwherein a partially rigid spacer preferably has a chain length of up to20-atoms, e.g. up to 10 atoms and comprises at least one rigid group asdefined above, particulary an alkyne group, and at least one flexiblegroup, e.g. an alkylene group. If on the other hand, the functionalgroup is an aldehyde group or a protected aldehyde group or an aldehydeprecursor group attachment via or a partially rigid spacer as definedabove or an at least partially rigid spacer having a chain length offrom 2 to 10 atoms is preferred. The structure of a rigidgroup-containing spacer, e.g. a partially rigid spacer, is preferablysuch that the rigid group is directly attached to the nucleobase. Apreferred example of a partially rigid spacer is shown in FIGS. 15 a andb.

The functionalized compound is capable of forming an association productwith the analyte to be detected. On the one hand, the functionalizedcompound may be selected from compounds which can be incorporated intonucleic acids or nucleic acid analogues, i.e. nucleic acid or nucleicacid analogue building blocks. Preferred examples for such compounds arenucleotides or nucleotide analogues, e.g. aldehyde-functionalizednucleotides or nucleotide analogues, Click-functionalized nucleotides ornucleotide analogues or photosensitizer-functionalized nucleotides ornucleotide analogues. On the other hand; the functionalized compound maybe selected from nucleic acids or nucleic acid analogues, e.g.aldehyde-functionalized nucleic acids or nucleic acid analogues,Click-functionalized nucleic acids or analogues orphotosensitizer-functionalized nucleic acids or analogues.

The term “nucleotide” according to the present invention particularlyrelates to ribonucleotides, 2′-deoxyribonucleotides or2′,3′-dideoxyribonucleotides. Nucleotide analogues may be selected fromsugar- or backbone modified nucleotides, particularly of nucleotideanalogs which can be enzymatically incorporated into nucleic acids. Inpreferred sugar-modified nucleotides the 2′-OH or H-group of the ribosesugar is replaced by a group selected from OR, R, halo, SH, SR, NH₂,NHR, NR₂ or CN, wherein R is C₁-C₆ alkyl, alkenyl or alkynyl and halo isF, Cl, Br or I. The ribose itself can be replaced by other carbocyclicor heterocyclic 5- or 6-membered groups such as a cyclopentane or acyclohexene group. In preferred backbone modified nucleotides thephospho(tri)ester group may be replaced by a modified group, e.g. by aphosphorothioate group or a H-phosphonate group. Further preferrednucleotide analogues include building blocks for the synthesis ofnucleic acid analogs such as morpholino nucleic acids, peptide nucleicacids or locked nucleic acids.

Aldehyde-, Click- or photosensitizer-functionalized nucleic acids may beoligonucleotides, e.g. nucleic acids having a length of up to 30nucleotide (or nucleotide analogue) building blocks or polynucleotideshaving a length or more than 30 nucleotide (or nucleotide analogue)building blocks. Preferably, the nucleic acids and nucleic analogues arecapable of specific binding to the analyte, e.g. capable of hybridizingwith a nucleic acid analyte under assay conditions. The minimum lengthis preferably 12 and more preferably 14 nucleotide (or nucleotideanalogue) building blocks.

Functionalized nucleic acid or nucleic acid analogue building blocks maybe incorporated into nucleic acids by standard techniques for chemicalsynthesis and/or by enzymatic incorporation. Chemical synthesis forexample may be carried out by standard phosphoramidite chemistry usingmodified nucleoside phosphoramidites as building blocks in standardsynthesis protocols. Other types of preferred building blocks forchemical synthesis include H-phosphonate or phosphorotriester modifiednucleosides.

On the other hand, modified nucleotides may be incorporated into nucleicacids by enzymatic methods. Surprisingly, it was found that aldehyde- orClick-functionalized nucleoside triphosphates are accepted as enzymesubstrates by nucleic acid synthesizing enzymes such as DNA polymerases,RNA polymerases, reverse transcriptases or telomerases. For example, itwas found that modified nucleoside triphosphates are accepted by DNApolymerases commonly used for primer extension and amplificationprotocols, e.g. thermostable DNA polymerases such as Taq polymerase,Vent polymerase, Pfx polymerase, Pwo polymerase, or Therminatorpolymerase as described in Example 7. Enzymes accept modifiedtriphosphates without loss in fidelity and allow a template-basedincorporation into nucleic acids such as DNA and RNA.

The method of the present invention provides various embodiments ofanalyte detection. For example, functionalized nucleic acid buildingblocks, e.g. nucleotides or nucleotide analogues, together withappropriate enzymes, may be provided which are enzymaticallyincorporated into a nucleic acid molecule which forms the associationproduct with the analyte. In the present invention, a single type offunctionalized nucleotide or a plurality of different types offunctionalized nucleotides may be employed. Alternatively oradditionally, a functionalized nucleic acid or nucleic acid analogue mayalready be present, which has been manufactured, e.g. by chemical orenzymatic synthesis, and which specifically binds, e.g. by hybridizationto the analyte to be detected.

In a preferred embodiment the method comprises a primer extensionreaction optionally in combination with subsequent nucleic acidamplification steps such as PCR. For example, at least one primermolecule may be provided which hybridizes under assay conditions with anucleic acid analyte to be detected or the complement thereof. The boundprimer is then extended wherein a detectable extension product isobtained which is indicative for the presence and/or amount of thenucleic acid analyte to be detected. According to this embodiment,functionalized primers and/or functionalized nucleotides or nucleotideanalogues for incorporation into the extension product may be used.

Alternatively and/or additionally the method of the invention maycomprise the use of functionalized hybridization probes which hybridizeunder the assay conditions with the nucleic acid analyte to be detectedor the complement thereof wherein the formation of a hybridizationproduct is indicative for the presence and/or amount of the nucleic acidanalyte to be detected.

The detection method of the invention may be carried out by any knownnucleic acid detection protocols, e.g. involving the use of solidsupports. For example, a solid support, e.g. a chip or array or aparticulate material such as a bead may be provided to which a captureprobe is bound capable of hybridizing to the analyte to be detected. Thesolid phase bound nucleic acid analyte may be detected by usingfunctionalized hybridization probes which hybridize with the nucleicacid analyte in a different sequence part as the capture probe does andsubsequent detection of the bound hybridization probe, e.g. with ametallization reagent. This method is particularly suitable for thediagnostic applications in the agricultural and clinical field, e.g. forthe detection of DNA and/or mRNA from plants, e.g. genetically modifiedplants, DNA from pathogens or plant pests etc.

In a specific embodiment, the detection may involve contacting theassociation product of the analyte and a functionalized compoundcomprising a photosensitizer group with a photosensitive medium, e.g. bytransferring a sample or sample aliquot in which an association productmay be present onto the photosensitive medium, e.g. by spotting,pipetting etc. Upon irradiation, an energy transfer from thephotosensitizer group to the photosensitive medium is effected such thatmarker groups such as metal, e.g. silver, nuclei are formed in thephotosensitive medium in the presence, but not in the absence, ofphotosensitizer groups. If necessary, the marker groups may be subjectedto a development procedure, e.g. a chemical or photochemical developmentprocedure according to photographic techniques. The photosensitivemedium may be any solid support or any supported material capable offorming marker groups, e.g. metal nuclei. Preferably, the photosensitivemedium is a light sensitive medium, such as light sensitive paper or alight sensitive emulsion or gel on a supportive material. Morepreferably the photosensitive medium is a photographic medium such asphotographic paper. Irradiation is carried out under conditions, e.g. ofwavelengths and/or intensity of irradiation light, under which selectivemarker group formation takes place in the presence of photosensitizergroups. Preferably, irradiation takes place with infrared light and/orwith long wave visible light, depending on the sensitivity of themedium. The irradiation wavelength may be e.g. 500 nm or higher, 520 nmor higher, 540 nm or higher, 560 nm or higher, 580 nm or higher forvisible light or 700 nm to 10 μm, for infrared light.

An important aspect of the invention is the detection of geneticvariabilities, e.g. single nucleotide polymorphisms (SNPs). The genomeof, for example humans, contains nucleotide sequence variations at anaverage frequency of up to 0.1%. Therefore, these variabilities provideexcellent markers for the identification of genetic factors contributingto complex disease susceptibility [16, 17]. Although there is a widerange of techniques available for the detection of SNPs, most of thesemethods are slow, require extensive instrumentation, and PCRamplification [18]. The present method, however, is both inexpensive andflexible enough to accommodate low, moderate and high-throughputscreening needs with high speed, sensitivity and efficiency. Severalpossibilities exist to label selectively only the fully matching or themismatching strands allowing to use the method of the invention for thedetection of SNPs.

For example, the detection of nucleic acid matches or mismatches, e.g.in SNPs, may comprise the use of functionalized hybridization probeswhich hybridize under the assay conditions with the nucleic acid analyteto be detected for the complement thereof and subjecting thehybridization product to a treatment procedure wherein a hybridizationproduct containing at least one mismatch is dissolved and wherein thepresence of an undissolved hybridization product is indicative for thepresence and/or amount of a nucleic acid which has a fully complementarysequence (i.e. no mismatch) to the hybridization probe.

The treatment for the dissolution of mismatch-containing hybridizationproducts may comprise a mismatch digestion treatment, i.e. the use ofmismatch detecting enzymes which cleave the hybridization productdepending on the presence of a mismatch. Suitable enzymes for such amismatch digestion treatment include mismatch-glycosylases such as thoseencoded by the genes hMSH2 and hMLH1 and Mut S, Mut L and Mut H.Additional proteins are MutY and Mig.Mth1. Mig.Mth1 cuts T out of a TGmismatch, MutY cuts out A in an AG mismatch and the enzyme TDG cuts outT in a TG mismatch.

Alternatively or additionally, mismatch-containing hybridizationproducts may be dissolved by a differential hybridization treatmentinvolving the adjustment of hybridization conditions, e.g. in view oftemperature, salt concentration and/or washing with dimethyl ammoniumchloride, wherein a mismatch containing hybridization product isdissolved and the fully complementary hybridization product remainsstable.

In a still further embodiment, mismatches, e.g. SNPs, may be determinedby enzyme-catalyzed selective primer elongation. For this purpose aprimer is provided, wherein the 3′ end of the primer is directly locatedupstream of a potential mismatch site on the template analyte. A primerextension is only possible when a nucleotide which is complementary tothe next base on the template is present. By selecting a single type offunctionalized nucleotide and determining whether it is incorporatedinto the primer or not, the base on the potential mismatch site can bedetermined.

The method of the invention comprises the detection of marker groupswhich are incorporated into an association product of the analyte with afunctionalized compound. The marker groups are preferably selected frommetal deposition-forming groups, e.g. aldehyde-functionalized groups,from fluorescent or fluorescence-forming groups or from redox activegroups.

The formation of metal depositions requires the treatment of aldehydegroups with a metallization reagent, e.g. a reagent comprising metalatoms and/or ions selected from Ag, Au, Bi, Cu, Pd or Pt which can beselectively deposited around aldehyde groups, e.g. by reduction.Preferably, the metallization reagent comprises an Ag⁺ salt such as anAg-ammonium complex, i.e. the Tollens reagent. Further preferredexamples of metallization reagents are Cu (NO₃)/I₂, platinum terpyridinecomplexes such as [Pt(terpy)Cl]Cl, Pd(OAc)₂ or KAuCl₄.

Further, the functionalized groups may also function as a handle toattach other marker groups such as fluorescent marker groups. Forexample, marker compounds with amino groups may be coupled to aldehydegroups by reductive amination in the presence of a reducing agent suchas sodium cyanoborohydride. Alternatively hydrazone or oxime formationmay be used to provide marker groups.

The detection of the marker groups may be carried out according to knownmethods. For example, metal depositions may be determined qualitativelyand/or quantitatively by optical methods and/or electrical methods. In apreferred embodiment, metal depositions on a solid surface may bedetermined by measuring electrical parameters, e.g. conductivity.Fluorescent marker groups may be determined qualitatively and/orquantitatively by known fluorescent measurement methods, e.g. excitationvia a suitable light source such as a laser and detecting the emittedfluorescent light.

In a further embodiment, the invention comprises the detection of markergroups which are site-specifically formed in a photosensitive medium inthe presence of photosensitizer groups in an association product of theanalyte with a functionalized compound. The photosensitizer groups arepreferably selected from fluorescent or luminescent groups. Thephotosensitizer groups can be incorporated directly into the associationproduct or via a handle, e.g. via a Click-reaction as explained above indetail. The photosensitive medium comprises groups which, whenirradiated in the presence of photosensitizer groups, form detectablemarker groups such as metal nuclei which can be developed according tostandard photographic techniques, e.g. by chemical or photochemicaldevelopment techniques.

The invention also relates to reagent kits for detecting analytes, e.g.nucleic acid analyte's in a sample which comprise a functionalizedcompound having attached at least one functional group as describedabove. Generally, the kit may comprise a compound of formula (III)

F—S—N

wherein

-   -   F is any functional group as described above, e.g. a group A as        defined in formula (I), a group. C as defined in formula (II)        and/or a photosensitizer group;    -   S is a spacer or a bond, preferably a covalent bond, and    -   N is a nucleic acid or nucleic acid analogue building block such        as a nucleosidic or nucleotidic compound.

The reagent kit may optionally contain an aldehyde forming reagent or asecond partner for a Click-reaction and marker or marker-formingreagents or a photosensitive medium. The kits are preferably used in amethod as indicated above.

Further, the present invention relates to an aldehyde-functionalizedcompound of formula (I) or a Click-functionalized compound of formula(II) as indicated above. The functionalized compounds may be buildingblocks for the chemical or enzymatic synthesis of nucleic acids ornucleic acid analogues or precursors thereof. Preferably, the compoundsare nucleoside triphosphates, particularly ribose, 2′-deoxyribose or2′-, 3′-dideoxyribose nucleoside triphosphates or analogues thereofwhich may be enzymatically incorporated into nucleic acids.

Furthermore, the compounds may be building blocks for the chemicalsynthesis of nucleic acids, or nucleic acid analogues such as peptidenucleic acids, morpholino nucleic acids or locked nucleic acids. To thisend nucleoside phosphoramidites, H-phosphonates, phosphotriesters orFmoc and/or Boc protected nucleobase amino acids are suitable.

The invention also relates to a nucleic acid or nucleic acid analoguemolecule having incorporated therein at least one compound of formula(I) and/or formula (II). The molecule may be a nucleic acid selectedfrom DNA and RNA or a nucleic acid analogue, e.g. selected from peptidicnucleic acids, morpholino nucleic acids or locked nucleic acids asdescribed in detail above.

Further, the invention relates to a method of synthesizing a nucleicacid or nucleic acid analogue molecule comprising incorporating at leastone nucleotide or nucleotide analogue building block comprising acompound (I) and/or (II) into a nucleic acid or nucleic acid analoguemolecule. The method may comprise a chemical synthesis and/or anenzymatic synthesis.

Furthermore, the invention relates to a metallization product of thenucleic acid or nucleic acid molecule as indicated above which isobtainable by treatment of an aldehyde functionalized compoundcontaining nucleic acid with a metallization reagent as indicated indetail above.

Furthermore, the invention relates to an association product of thenucleic acid or nucleic acid analogue molecule as indicated above withan analyte as described above. Preferably, the association product is ahybridization product with a complementary nucleic acid.

In a preferred embodiment, the methods and the reagent kits of thepresent invention are used for agricultural applications. For example,the invention is suitable for the detection of nucleic acids fromplants, plant pathogens or plant pests such as viruses, bacteria, fungior insects. Further, the invention is suitable for detecting geneticvariabilities, e.g. SNPs in plants or plant parts, plant pathogens orplant pests such as insects.

A further application is a detection or monitoring of herbicide,fungicide or pesticide resistances, tolerances or intolerances, e.g.resistances, tolerances or intolerances in fungi, insects or plants inorganisms or populations of organisms. The invention is also suitablefor rapid genotyping, e.g. for the rapid detection and/ordifferentiation of species or strains of fungi, insects, or plants.Further, detection and/or differentiation of genetically modifiedorganisms for strains, e.g. organisms or strains of fungi, insects orplants is possible.

Due to the high sensitivity of the invention, early diagnostic ofpathogens is possible, i.e. diagnostics before first symptoms of thepresence of pathogens is visible. This is particularly important for thediagnosis of soy rust (Phakospora pachyrizi) or other pathogens, e.g.Blumeria graminis, Septoria tritici or Oomycetes or other pathogens forwhich control is only possible, if their presence is detected before itcan be visually recognized.

Further, the invention is suitable for medical, diagnostic and forensicapplications, e.g. in human or veterinary medicine, e.g. for thedetection of nucleic acids from pathogens, e.g. human pathogens orpathogens of livestock or pet animals.

Further preferred applications include the detection of geneticvariabilities, e.g. SNPs in humans or the detection of medicamentresistances, tolerances or intolerances or allergies. Further, theinvention is suitable for genotyping, particularly genotyping of humansin order to determine mutations associated with predisposition orenhanced risk of disorders, allergies and intolerances.

The invention may also be used for the detection of genetically modifiedorganisms or strains, organisms or strains of bacteria or viruses butalso genetically modified life stock animals etc. The invention isparticularly suitable for the rapid diagnosis of diseases, e.g. geneticdiseases, allergic diseases, autoimmune diseases or infectious diseases.

Furthermore, the invention is suitable for detecting the function and/orexpression of genes, e.g. for research purposes.

Still a further embodiment is the use of the method for brandprotection, e.g. for detecting specific information encoded in productssuch as valuable goods like plant protection products, pharmaceuticals,cosmetics and fine chemicals (e.g. vitamins and amino acids) andbeverage products, fuel products, e.g. gasoline and diesel, consumerelectronic appliances can be marked. Further, packaging of these andother products can be marked. The information is encoded by nucleicacids or nucleic acid analogues which have been incorporated into theproduct and/or into the packaging of a product. The information mayrelate to the identity of the manufacturer, to production sites, date ofproduction and/or distributor. By means of the present invention, rapiddetection of product-specific data can be carried out. A sample may beprepared from an aliquot of the product which is then contacted with oneor several sequence-specific functionalized hybridization probes capableof detecting the presence of nucleic acid-encoded information in thesample.

The invention is also suitable for the field of nutrients. For example,in the feed area, animal nutrients, e.g. corn, are supplemented with agreater quantity of preservatives such as propionic acid. By applyingthe method of the invention, the addition of preservatives can bereduced. Further, genomic analysis with the method of the inventionallows the prediction of an individual's capability to utilize specificnutrients (nutrigenomics).

Still a further preferred embodiment refers to the field of epigenetics.This embodiment particularly refers to an analysis of DNA, e.g. genomicDNA with regard to methylation of cytosine bases. In this embodiment,the DNA may be treated with a cytosine-specific reagent, e.g. hydrazineand/or hydroxylamine. By means of the treatment, a selective reaction ofeither cytosine or methylcytosine residues occurs. For example,treatment with hydroxylamine leads to a selective modification ofcytosine residues. Preferably, the reagent is added in asub-stoichiometric amount in order to obtain a partial modification ofe.g. cytosine residues. Subsequently, the treated DNA is analysed, e.g.by a primer extension reaction using at least one modified nucleic acidbuilding block as indicated above, e.g. a dU and/or dC base. Preferablya Click-modified base, e.g. an alkyne-modified base is used. The primerextension reaction gives a characteristic sequencing ladder resultingfrom interruptions of the reaction on the modified dC or 5-methyl-dCbases (cf. FIG. 26).

A further preferred embodiment refers to the application of reporternucleic acid molecules to a photosensitive medium, e.g. photographicpaper or any other light sensitive medium. Preferably, the reportermolecules carry a photosensitizer group and a quencher group. In theabsence of analyte the photosensitizer group is quenched. For example,the reporter molecule may have a hairpin structure with thephotosensitizer and the quencher group on or near the termini of themolecule in close spatial relation-ship. When the reporter molecule ispresent as a hairpin structure, the photosensitizer group is quenched(according to the known molecular beacon technique). Thus, a reportermolecule with an intact hairpin structure cannot effect asensibilisation when irradiating light to the photosensitize medium. Inthe presence of an analyte the hairpin structure is broken up. Theanalyte may be a complementary nucleic acid strand or an enzyme whichcleaves the hairpin structure or a protein which binds to the hairpinand thus brakes up the structure. The photosensitizer group is separatedfrom the quencher group and thus is capable of photosensibilisation. Inthis case, irradiation of light leads to a sensibilisation of thephotographic medium and thus to the detection of analyte (cf. FIG. 27).

In this embodiment the present invention relates to a method fordetecting an analyte in a sample comprising the steps:

-   i providing a sample,-   ii providing a reporter molecule comprising a photosensitizer group    or a handle group for introducing a photosensitizer group and a    quencher group wherein the photosensitizer group is quenched in the    absence of the analyte to be detected,-   iii contacting the sample with the reporter molecule under    conditions wherein the quenching of the photosensitizer group is at    least partially reduced or terminated in the presence of the    analyte,-   iv if necessary, reacting the handle group with a reaction partner    comprising a photosensitizer group,-   v irradiating said reporter molecule in contact with a    photosensitive medium under conditions wherein marker groups are    formed in said photosensitive medium in the presence of unquenched    photosensitizer groups in said reporter molecule, and-   vi detecting said marker groups

Further, this embodiment refers to a reagent kit for detecting ananalyte in a sample comprising

-   a a reporter molecule comprising a photosentisitizer group or a    handle group for introducing a photosensitizer group and a quencher    group wherein the photosensitizer group is quenched in the absence    of the analyte to be detected,-   b optionally a reaction partner for the handle group comprising a    photosensitizer group and-   c a photosensitive medium which forms marker groups upon irradiation    of unquenched photosensitizer groups

Preferred aspects of the method an the reagent kits and preferredapplications are as described above.

The invention is further explained by the following Figures andExamples.

DESCRIPTION OF FIGURES

FIG. 1: Preferred attachment sites of functional groups (R), e.g.aldehyde functionalized groups on different nucleobases 7-dN-G, C,7-dN-A and T for the enzymatic incorporation of marker groups intooligonucleotides.

FIG. 2: Schematic representation of the synthesis of aldehydefunctionalized nucleoside building blocks for the solid phase synthesisof nucleic acids.

FIG. 3 a: Schematic representation of the synthesis of an acetal(protected aldehyde) functionalized nucleoside triphosphate for theenzymatic synthesis of nucleic acids.

FIG. 3 b: An example of an alkyne functionalized nucleoside triphosphatefor efficient Click chemistry in DNA, wherein n is preferably 0-4.

FIG. 3 c: An example of a protected aldehyde functionalizedtriphosphate. The compounds shown in FIG. 3 are suitable for efficientPCR incorporation into DNA.

FIG. 4: The results of a metallization reaction by contacting Tollensreagent with an aldehyde-modified base: (1) sugar solution as reference,(2) DNA with one aldehyde-modified group, (3) DNA with two aldehydegroups and (4) unmodified DNA.

FIG. 5: (I) Primer extension products stained with Ag (a) or using astandard fluorescence dye (b): I.1a: aldehyde-modified TTP in primerextension. I.1b: acetal-modified TTP in primer extension. I.3a:unmodified DNA. Silver staining only positive on Lane 1 and 2. I.1b-3bsame gel but stained unspecifically with a fluorescence dye. (II) A 2142by PCR product stained with a fluorescent dye (a) or with Ag (b): II2a:acetal-modified TTP in PCR. M: marker; II1b: aldehyde-modified TTP inPCR, 2: acetal-modified TTP in PCR, II3b: unmodified DNA.

FIG. 6: The results of a dilution series with a synthetic DNA moleculecontaining a single aldehyde functional group. Detection by Ag-staining.

FIG. 7: Examples of nucleosides with different nucleobases carryingacetal (protected aldehyde) functions, which can be converted intocorresponding phosphoramidites, H-phosphonates or triesters for chemicalsynthesis of nucleic acids or into 5′-triphosphates for enzymaticincorporate of nucleic acids.

FIG. 8: Derivatisation of aldehyde modified DNA or PNA with afluorescence tag as an alternative to metallization via reductiveamination.

FIG. 9: Alkyne-modified (a,b), azide-modified (c) and protectedaldehyde-modified (d,e) nucleoside and nucleotide monomers, wherein n ispreferably 0-4.

FIG. 10: Schematic representation of the synthesis ofalkyne-functionalized nucleosides and nucleotide triphosphates.

FIG. 11: Schematic representation of the synthesis ofazide-functionalized dendrimers comprising protected aldehyde groups.

FIG. 12: Examples of azide and alkyne azide derivatives with marker ormarker precursor groups for the Click reaction with alkyne- orazide-modified nucleotides or nucleic acids.

FIG. 13: On top: MALDI-TOF analysis of the Click reaction witholigonucleotides containing the modified base 2 (FIG. 9 b) andfluorescein azides as the clicking partner (m: 495). Below: Gelelectrophoresis of Click reactions of DNA modified with monomer 2 andfluorescine azide. A1: Fluorescence image, Lane 1: starting materialprior to Click reaction; 2,3: raw reaction mixture; 4: Azide under Clickconditions; A2: same gel stained with SYBR Green. B1: Lane 1,2: rawreaction mixture; 3: starting material; B2 same gel but stained stainedwith SYBR Green.

FIG. 14: Click reaction for introducing coumarin azide into DNA resultsin a fluorescent product (right reaction tube).

FIG. 15: An alkyne-modified phosphoramidite (a), an alkyne-modifiednucleoside (b) and azide-modified galactose (c).

FIG. 16: PCR assay using 200 μM of 8, dATP, dCTP and dGTP, 0.05 μggenomic DNA from S. cerevisiae 499, 10× polymerase buffer withmagnesium, 0.3 mM each of primers and 1.25 U polymerases. Lane1) Vent,2) Vent (exo⁻), 3) Pwo, 4) Taq (exo⁻) from Roche, 5) Therminator, 6) Taqfrom Promega and 7) marker.

FIG. 17: PCR amplification of 2142 by DNA with modified triphosphate 1or 8 (FIG. 10) replacing dTTP. Agarose Gel (2%) was used and stainedwith Ethidium Bromide. A total of 35 PCR cycles were run, with 45 secused for each incubation. Lane 1) NEB 2-log DNA ladder (0.1-10.0 kb),Lane 2) Negative control (minus dTTP), Lane 3) with substrate (1)replacing dTTP, 4) with substrate (8) replacing dTTP and 5) positivecontrol (using dTTP).

FIG. 18: HPLC chromatogram of (a) the enzymatic digest of PCR fragments(318 mer) incorporating triphosphate 8 (FIG. 10); (b) the enzymaticdigest of PCR fragments incorporating dTTP; (c) nucleoside 7 (FIG. 10).

FIG. 19: Dilution series of 318 by PCR fragments incorporatingtriphosphates 1 and 2 followed by “on the gel” clicking and silverstaining. (a) Dilution series of PCR fragments incorporating 1 (Lane 17.0 ng, Lane 2 3.5 ng, Lane 3 1.3 ng, Lane 4 0.7 ng) and 2 (Lane 5 7.0ng, Lane 6 3.5 ng, Lane 7 1.3 ng, Lane 8 0.7 ng) run on a TBE-urea PAAGgel. The gel was subjected to “on the gel” clicking with azide 3 andsubsequent silver staining. (b) Comparative detection of a dilutionseries of a PCR fragment incorporating 2 via (i) the selective silverstaining method (as per (a)) and via (ii) SYBR green II (Lane 1 7 ng,Lane 2 3.5 ng, Lane 3 1.3 ng, Lane 4 0.9 ng, Lane 5 0.5 ng, Lane 6 0.3ng). (c) Dilution series of PCR fragments incorporating 2 (Lane 1 7 ng,Lane 2 3.5 ng, Lane 3 1.3 ng, Lane 4 0.9 ng, Lane 5 0.5 ng, Lane 6 0.3ng) and 2 Lane 1 7.0 ng, Lane 2 3.5 ng, Lane 3 1.3 ng, Lane 4 0.7 ng)run on TBE-urea PAAG gel. The gel was then subjected to “on the gel”clicking with aldehyde-modified azide 4 and subsequent silver staining.(d) Dilution series of PCR fragments incorporating 2 (Lane 1 7 ng, Lane2 3.5 ng, Lane 3 1.3 ng, Lane 4 0.9 ng, Lane 5 0.5 ng, Lane 6 0.3 ng)run on TBE-urea PAAG gel. The gel was then subjected to “on the gel”clicking with aldehyde-modified azide 5 and subsequent silver staining.

FIG. 20: AFM photographs of natural DNA (a) and aldehyde-modified DNA(b) after exposure to Ag staining conditions, and aldehyde-modified DNAafter Ag staining without development (c), after 2 min of development(d) and after two times 2 min of development (e).

FIG. 21: A schematic depiction of an analyte, e.g. DNA analyte detectionmethod using the principles of black and white photography. Initialreplication of the DNA analyte in the presence of a sequence-selectiveprimer produces a target sequence tagged with a sensitizer (S). Afterirradiation and subsequent photographic development the analyte can bedetected on a photosensitive medium, e.g. photographic paper.

FIG. 22: Depiction of cyanine dyes (1), (2) and (3). Dilution series ofcyanine dyes irradiated for 10 seconds using an overhead projector lampequipped With a 520 nm cut-off filter using (a) 1; (b) 2; and (c) 3 orirradiation for 5 minutes with an infrared lamp using (d) 1, (e) 2 and f(3). The spot experiments correspond to the following dilutions:Spot1:1×10⁻¹¹ mol., Spot 2: 1×10⁻¹² mol., Spot 3: 3×10⁻¹³ mol, Spot 4:1×10⁻¹³ mol, Spot 5: 3×10⁻¹⁴ mol, Spot 6: 1×10⁻¹⁴ mol, Spot 7: 3×10⁻¹⁵mol, Spot 8: 1×10⁻¹⁵ mol, Spot 9: 3×10⁻¹⁶ mol, Spot 10:1×10⁻¹⁶ mol,

FIG. 23: Spot tests of oligodeoxyribonucleotides ODN-I [5′-GCG ATT CGTTCG TCG C-3′] (SEQ ID NO: 1), ODN-2 [5′-CGC GAA TGA ACA GCG C-3′] (SEQID NO: 2) and ODN-3 [5′-GCG ACC GAT TCG C-3′] (SEQ ID NO: 3) all at 50nmol. using (a) high energy irradiation and a cut-off filter (520 nm);and (b) low energy irradiation via prolonged exposure (5 minutes) usingan infrared lamp.

FIG. 24: Depiction of cyanine dyes Cy5 and Cy5.5. Dilution series ofcyanine dyes tethered to ODNs irradiated for either 10 seconds using anoverhead projector lamp equipped with a 520 nm cut-off filter using (a)ODN-4 [5′-Cy5-GCG CTG TTC ATT CGC G-3′] (SEQ ID NO: 4); (b) ODN-5[5′-Cy5.5-GCG CTG TTC ATT CGC G-3′] (SEQ ID NO: 5); or irradiation for 5minutes with an infrared lamp using (c) ODN-4; (d) ODN-5. The spotexperiments correspond to the following dilutions: Spot 1: 1×10⁻¹¹ mol.,Spot 2: 3×10⁻¹² mol., Spot 3: 1×10⁻¹² mol, Spot 4: 3×10⁻¹³ mol, Spot 5:1×10⁻¹³ mol, Spot 6: 3×10⁻¹⁴ mol, Spot 7: 1×10⁻¹⁴ mol, Spot 8: 3×10⁻¹⁵mol.

FIG. 25: Schematic depiction of the process of the “Click andphotograph” methodology. A sequence, e.g. gene, of interest isspecifically selected and amplified via PCR with alkyne-modifiedtriphosphates (dU*TP) and gene-selective primers. These alkyne functionscan be tagged via click chemistry with an appropriate photosensitizer(S) producing photosensitized DNA hybrids. Irradiation of the sample onphoto paper and subsequent development will provide a new method for theultra sensitive and specific detection of genes.

FIG. 26: Schematic depiction of a method for identifying methylationpatterns in DNA by cytosine-specific chemical modifications. A DNAanalyte is reacted with a cytosine (or methylcytosine) specificmodification agent, e.g. hydroxylamine, preferably in asub-stoichiometric amounts in order to give partially modified cytosineresidues (C*). A primer extension reaction with an alkynyl-modified baseis carried out. This reaction terminates at modified cytosine residuesresulting in a “ladder” of extension products having a characteristiclength. After separating the primer extension products e.g. on a gel, aClick reaction with an azide-modified marker group, e.g. a modifiedsugar and a subsequent detection of the marker group (e.g. via silverstaining) is carried out. The methylation pattern of the DNA sample maybe determined by comparing extension products from a methylated DNAsample with the extension products from an unmethylated DNA sample whichhas been subjected to the same treatment.

FIG. 27: Schematic depiction of a molecular beacon detection method on aphotosensitive medium. A reporter molecule having a fluorescence group(F) and a quenching group (Q) is provided. In the absence of analyte,the reporter molecule has a hairpin structure and the fluorescence isquenched. In the presence of analyte the quenching group is removed fromthe fluorescence group which becomes unquenchend (F*). The sample isirradiated in the presence of a photographic medium such as photographicpaper or other light-sensitive material and developed.

EXAMPLES Example 1 Synthesis of Aldehyde-modified Nucleosides andNucleotides

Nucleosides and nucleoside triphosphates with aldehyde-modifiednucleobases were synthesized from appropriately modified nucleosideswhich carry a leaving group such as I, preferably either on position 5of pyrimidine bases, e.g. T, U and C or on position 7 of purine bases,e.g. 7-desaza G, 7-desaza A, G and A as shown in FIG. 1. Allmodifications on these positions protrude out of the DNA major groove.

The synthesis of an aldehyde-modified T (U) nucleoside phosphoramiditefirst via Sonogashira mediated alkynylation [20] followed by reactionwith appropriate functional groups was performed as shown in FIG. 2. Thealdehyde function was kept protected as an acetal group. The acetalprotection group may be removed by treatment with acid. The modifiednucleoside phosphoramidite may be incorporated into nucleic acids bychemical synthesis.

The synthesis of an acetal-modified nucleoside triphosphate was carriedout as shown in FIG. 3 a. Further alkyne (for Click reaction), acetal-and hemiacetal-modified nucleoside triphosphates are shown in FIG. 3 b.The modified nucleoside triphosphates may be incorporated into nucleicacids by enzymatic synthesis.

The use of Pd-based C—C forming reactions such as by Sonogashira/Suzuki[20] provides a general synthetic approach for the synthesis ofaldehyde-modified nucleosides and nucleotides with different aldehydegroups with different modified nucleobases. Further, aldehyde groupswith different steric, electronic and functional characteristics may besynthesized.

Example 2 Incorporation of Aldehyde-modified Nucleosides and Nucleotidesinto Oligonucleotides 2.1 Incorporation by Chemical Synthesis

Incorporation of the acetal/aldehyde-modified nucleoside phosphoramiditewas achieved by conventional solid phase synthesis [21]. Several DNAoligonucleotides containing one or multiple acetal/aldehyde-modifiednucleobases were prepared as depicted in Table 1. Deprotection of theacetal groups afforded the aldehyde-modified DNA oligonucleotide.

The oligonucleotides were tested for their ability to form base pairswith complementary DNA strands in order to obtain double stranded DNAmolecules. It was found that the reduction of duplex stability due tothe presence of the aldehyde group is low. The melting point of doublestrands is lowered by about only 2° C. per modification. This amount ofdestabilisation is, however, fully acceptable for the intendedapplications.

TABLE 1 Oligodesoxynucleotides synthesised by solid  phase synthesis (SEQ ID NOS: 6-10, re-spectively, in order of appearance). T_(m) [° C.] 1 TTTTTTXTTTTT 2TTTTTTXXTTTTT 3 GCCGAXGCGC 53.8 (56.5 unmodified control) 4GCGXATAXATAXTCGC 48.4 (53.7 unmodified control) 5 TTXTTXTTXTTXTTX

2.2 Incorporation by Enzymatic Methods

Acetal modified triphosphate monomers were prepared according to FIG. 3.The most selective method of synthesising triphosphates is the procedurefollowing Ludwig and Eckstein [11, 12]. This procedure is slightlyacidic so one obtains a mixture of aldehyde and acetal-TTP which can beseparated by HPLC, if desired [13].

Studies were performed with both the acetal and aldehyde triphosphatesand a variety of different DNA polymerases. They showed that allpolymerases accept the modified triphosphate as substrate and theyselectively incorporate the modified base. Also multiple incorporationsturned out to be unproblematic. The following polymerases were tested inprimer extension studies and PCR. The experiments were performed withthe acetal protected thymidine and also with the deprotected aldehydefunctionalized thymidine.

Primer extention PCR Therminator (NEB) Pfx (A) Vent Taq (A) Vent (exo⁻)Vent (B)

Taq

We also performed PCR studies with TPP replaced by the synthetictriphosphates (acetal and aldehyde). The PCR experiment showed that themodified base can be incorporated into a whole gene 2400 base pairs longestablishing that we can create genes specifically labelled withhundreds of aldehyde derived nucleation sites.

Example 3 Detection of the Labelled Oligonucleotides and Genes

A preferred method for the metal deposition on aldehydes is based on theTollens test [14].

R—CHO+2 Ag[NH₃]OH→R—COO⁻NH₄ ⁺+2 Ag(s)+H₂O+NH₃

In this reaction a silver-ammonium complex is reduced by the aldehyde.If the concentration of the aldehyde is high, one can see a film ofsolid silver on the inside of the reaction tube.

Both the aldehyde containing nucleoside and the chemically synthesisedaldehyde-modified nucleic acids could be detected in a silver stainingtest indicative of aldehyde functions (FIG. 4). An unlabeled DNA strandgave in contrast a clearly negative result under the same conditions,showing that the aldehyde selectively introduced into specific DNAsequences allow selective detection of these modified sequences.

Detection of aldehyde-modified nucleic acids by silver staining was alsocarried out on gels. The aldehyde groups on the DNA were sufficient toreduce the silver ions within a gel. The seeds formed by the process onthe DNA could be developed until a clear black band made up fromdeposited silver can be seen on the gel.

This was demonstrated by staining aldehyde-modified nucleic acids fromprimer extension reactions and from PCR (FIG. 5 (I) and (II)respectively).

As shown in FIG. 5, the DNA containing the modified nucleoside isexclusively Ag-stained while unmodified DNA stays unstained. This istrue for the extended primer and for the PCR product. The stainingprocedure is based on the SilverXPress kit (Invitrogen), but with astronger Tollens solution. Staining following other procedures is alsopossible.

Example 4 Determination of Sensitivity

In order to determine the sensitivity of the detection method, dilutionexperiments were performed (FIG. 6). It was found that staining ofaldehyde-functionalized DNA with a standard Ag staining kit was at leastfive times more sensitive than staining with ethidium bromide (˜0.5 ngof DNA with a length of 50 bp).

This very impressive sensitivity is obtained even with coarse visualdetection.

Example 5 Synthesis of Azide- and Alkyne-modified Nucleosides andNucleotides

Nucleosides and nucleoside triphosphate with azide and alkyne-modifiedbases were synthesized substantially as described in Example 1.

5. 1 Synthesis of Alkyne-modified Nucleotides

A detailed reaction scheme for the synthesis of alkyne-modifiednucleoside triphosphate is shown in FIG. 10.

The preparation of nucleoside (1) and its corresponding triphosphate (2)was carried out as previously [23, 24].

To a thoroughly degassed solution of 3 (1.00 g, 1.72 mmol.),^([3)]Pd(PPh₃)₄ (0.198 g, 0.172 mmol.) and CuI (0.065 g, 0.344 mmol.) in DMF(3 mL) was added degassed N,N-diisopropylethyl amine (1.5 mL, 8.59mmol.) and the reaction mixture stirred at room temperature for 10minutes. A degassed solution of 4-pentyn-1-ol (320 μL, 3.44 mmol.) inDMF (1 mL) was added dropwise to the reaction mixture over 1 hour. Aftercomplete addition, the reaction mixture was stirred at room temperatureovernight. After concentration in vacuo, the crude mixture was dilutedwith ethyl acetate (200 mL) and the organic layer was washed with brine(3×50 mL) followed by water (50 mL). The organic layer was dried(MgSO₄), filtered and concentrated in vacuo. Flash column chromatography(SiO₂) eluting with a gradient of ethyl acetate:isohexane (1:1) followedby ethyl acetate:isohexane (2:1) provided 4 (0.790 g, 86%) as a paleyellow foam. ¹H NMR (CDCl₃, 300 MHz): δ 0.01 (s, 3 H, OSiCH₃), 0.00 (s,3 H, OSiCH₃), 0.05 (s, 3 H, OSiCH₃), 0.07 (s, 3 H, OSiCH₃), 0.81 (s, 6H, OSi(CH₃)₃), 0.85 (s, 6 H, OSi(CH₃)₃), 1.74 (m, 2H, CH₂—CH₂CH₂—OH),1.95 (m, 1H, H-2β), 2.20 (m, 1H, H-2α), 2.42 (t, 2H, J=6.0 Hz,C≡C—CH₂CH₂—), 3.67 (dd, 1H, J=11.4, 2.1 (CDCl₃, 75.5 MHz): δ 5.4(SiCH₃), −5.3 (SiCH₃), −4.8 (SiCH₃), −4.6 (SiCH₃), 16.7 (C≡C—CH₂CH₂),18.0 (SiC(CH₃)₃), 18.5 (SiC(CH₃)₃), 26.1 (SiC(CH₃)₃), 26.4 (SiC(CH₃)₃),31.5 (CH₂—CH₂—CH₂—OH), 42.3 (C-2′), 61.9 (CH₂—CH₂CH₂—OH), 63.3 (C-5′),72.4 (C≡C), 72.7 (C-3′), 86.0 (C-1′), 88.7 (C-4′), 95.0 (C≡C), 100.9(C-5), 101.0 (C≡C), 141.9 (C-6), 149.6 (C-2), 162.4 (C-4). HRMS (ESI,+ve) calcd. for C₂₆H₄₆N₂NaO₆Si₂ 561.2792 [M+Na]⁺ found 561.2803.

To a stirred solution of 4 (0.300 g, 0.56 mmol.) in dichloromethane (5mL) was added a solution of Dess-Martin periodinane (0.378 g, 0.89mmol.) in dichloromethane (5 mL) dropwise over 5 minutes at roomtemperature under a nitrogen atmosphere. The reaction mixture wasstirred for 2 hours followed by quenching with saturated sodiumthiosulfate solution (10 mL). The crude mixture was then diluted withdichloromethane (200 mL) and the organic layer washed with brine (2×30mL) and water (2×30 mL). The organic layer was then dried (MgSO₄),filtered and concentrated in vacuo. Column chromatography (flash silica)eluting with 35% ethylacetate in isohexane afforded 5 (0.193 g, 65%) asa pale yellow foam. ¹H NMR (CDCl₃, 600 MHz): δ0.07 (s, 3 H, OSiCH₃),0.00 (s, 3 H, OSiCH₃), 0.05 (s, 3 H, OSiCH₃), 0.06 (s, 3 H, OSiCH₃),0.81 (s, 6 H, OSi(CH₃)₃), 0.85 (s, 6 H, OSi(CH₃)₃), 1.95 (m, 1H, H-2β),2.21 (m, 1H, H-2α), 2.61 (t, 2H, J=7.2 Hz, —CH₂CH₂—), 2.67 (t, 2 H,J=7.2 Hz, —CH₂CH₂—), 3.68 d(d, 1H, J=11.4, 2.4 Hz, H-5′), 3.81 (dd, 1H,J=11.4, 2.4 Hz, H-5′), 3.89 (m, 1H, H-4′), 4.32 (m, 1H, H-3′), 6.20 (dd,1 H, J=7.2, 6 Hz, H-1′), 7.84 (s, 1H, H-6), 8.99 (bs, 1H, N—H), 9.72 (s,1H, CHO). ¹³C NMR (CDCl₃, 150.8 MHz): 63.8 (SiCH₃), −3.7 (SiCH₃), −3.1(SiCH₃), −2.9 (SiCH₃), 14.4 (C≡C—CH₂CH₂), 19.7 (SiC(CH₃)₃), 20.1(SiC(CH₃)₃), 27.4 (SiC(CH₃)₃), 27.7 (SiC(CH₃)₃), 43.7 (C-2′), 44.1(CH₂—CH₂—CHO), 64.6 (C-5′), 74.0 (C-3′ and C≡C), 87.5 (C-1′), 90.0(C-4′), 94.3 (C≡C), 101.9 (C-5), 143.8 (C-6), 150.9 (C-2), 163.7 (C-4),201.6 (CHO). HRMS (ESI, +ve) calcd. for C₂₆H₄₄N₂NaO₆Si₂ 559.2635 [M+Na]⁺found 559.2634.

To a solution of 5 (0.530 g, 1.00 mmol.) and K₂CO₃ (0.269 g, 1.98 mmol.)in dry methanol (20 mL) was added a solution of1-diazo-2-oxo-propyl-phosphonic acid dimethyl ester (0.261 g, 1.19mmol.) in dry methanol (5 mL) at room temperature under a nitrogenatmosphere. The reaction mixture was stirred at room temperatureovernight, filtered and concentrated in vacuo. The crude mixture wasdissolved in ethyl acetate (200 mL) and the organic layer was washedwith brine (2×30 mL) and water (2×30 mL), dried (MgSO₄) and concentratedin vacuo. Column chromatography (flash silica) eluting with 20%ethylacetate in isohexane afforded 6 (0.290 g, 55%) as a colourlessfoam. ¹H NMR (CDCl₃, 600 Mhz): δ 0.00 (s, 3 H, OSiCH₃), 0.01 (s, 3 H,OSiCH₃), 0.06 (s, 3 H, OSiCH₃), 0.07 (s, 3 H, OSiCH₃), 0.82 (s, 6 H,OSi(CH₃)₃), 0.86 (s, 6 H, OSi(CH₃)₃), 1.93 (m, 1H, H-213), 1.95 (s, 1H,C≡C—H), 2.22 (m, 1H, H-2α), 2.39 (dt, 2H, J=8.4, 2.4 Hz, —CH₂CH₂—), 2.55(t, 2H, J=8.4 Hz, —CH₂CH₂—), 3.68 (dd, 1H, J=11.4, 2.4 Hz, H-5′), 3.81(d, 1H, J=11.4, 2.4 Hz, H-5′), 3.89 (m, 1H, H-4′), 4.33 (m, 1H, H-3′),6.20 (dd, 1H, J=7.8, 6 Hz, H-1′), 7.85 (s, 1H, H-6), 8.33 (bs, 1H, N—H).¹³C NMR (CDCl₃, 150.8 MHz): 67.0 (SiCH₃), −6.9 (SiCH₃), −6.4 (SiCH₃),−6.2 (SiCH₃), 16.5 (C≡C—CH₂CH₂), 16.9 (C≡C—CH₂CH₂), 17.0 (SiC(CH₃)₃),18.2 (SiC(CH₃)₃), 24.2 (SiC(CH₃)₃), 24.5 (SiC(CH₃)₃), 40.4 (C-2′), 61.4(C-5′), 67.9 (C≡C—H), 70.8(C-3′), 70.9 (C≡C), 80.9 (C≡C), 84.1 (C-1′),86.8 (C-4′), 91.2 (C≡C), 98.7 (C-5), 140.6 (C-6), 147.5 (C-2), 159.9(C-4). HRMS (FAB, +ve) calcd. for C₂₇H₄₃N₂O₆Si₂+H 533.28670 [M+H]⁺found533.26009.

To a cooled solution (0° C.) of 6 (0.270, 0.51 mmol.) in THF (5 mL) wasadded TBAF (1.0 M, 1.52 mL, 1.52 mmol.) under a nitrogen atmosphere. Thereaction mixture was stirred for 3 hours, quenched with glacial aceticacid (1.0 mL) and concentrated in vacuo. Column chromatography (flashsilica) eluting with 10% methanol in ethyl acetate afforded 7 (0.127 g,82%) as a colourless oil. ¹H NMR (d₆-DMSO, 400 MHz): 61.88 (s, 1H,C≡C—H), 2.07 (m, 2H, H-2′), 2.36 (dt, 2H, J=7.2, 2.4 Hz, —CH₂CH₂—), 2.54(t, 2H, J=6.8 Hz, —CH₂CH₂—), 3.53 (dd, 1H, J=12.0, 4.0 Hz, H-5′), 3.58(dd, 1H, J=12.0, 4.0 Hz, H-5′), 3.76 (m, 1H, H-4′), 4.19 (m, 1H, H-3′),5.07 (bs, 1H, O—H), 5.23 (bs, 1H, O—H), 6.08 (t, 1H, J=6.4 Hz, H-1),8.11 (s, 1H, H-6), 11.55 (bs, 1H, N—H). ¹³C NMR (CDCl₃, 150.8 MHz): δ17.6 (C≡C—CH₂CH₂), 18.9 (C═C—CH₂CH₂), 39.5 (C-2′), 60.7 (C-5′), 70.0(C-3′), 73.7 (C≡C—H), 75.1 (C≡C), 84.6 (C-1′), 87.3 (C-4′), 89.1 (C≡C),93.0 (C≡C), 100.2 (C-5), 144.7 (C-6), 151.0 (C-2), 163.2 (C-4). HRMS(FAB, +ve) calcd. for C₁₅H₁₆N₂O₆+Na [M+Na]⁺327.28771 found 327.09635.HRMS (FT-ICR MS -) calcd. for C₁₅H₁₆N₂O₅+AcO⁻ [M+AcO⁻]⁻ 363,1198 found363,1221, MS-MS calcd. for C₁₅H₁₅N₂O₅ ⁻[M⁻] 303,1 found 303,1.

To a cooled solution (0? C) of 7 (0.060 g, 0.197 mmol.) and1,8-bis(dimethylamino)naphthalene (proton sponge, 0.068 g, 0.316 mmol.)trimethyl phosphate (2 mL) was added phosphorous oxychloride (22 μL,0.237 mmol.) dropwise over 5 min. under a nitrogen atmosphere. Thereaction mixture was stirred for 3 hours at 0? C. A solution oftributylammonium pyrophosphate (0.080 g, 0.237 mmol.) in dry DMF (2.0mL) was added to the reaction mixture and stirred for 1 min. followed byquenching with triethylammonium bicarbonate (1.0 M, 20 mL, pH=8.5). Thereaction mixture was stirred for 2 h and lyophilised overnight. RP-HPLCpurification (0-50% 0.1 M triethylammonium acetate ? 20:80 H₂O:MeCN with0.1 M triethylammonium acetate gradient over 45 min. at a flow rate of 5mL.min.⁻¹) yielded 8 (17.7 min.) as the triethylammonium salt. ³¹P NMR(D₂O, 81 MHz): δ 22.4 (t, 1 P, J=19.8 Hz, P-β), −10.5 (d, 1 P, J=20.3Hz, P-α), −9.7 (d, 1 P, J=19.8 Hz, P-γ). MALDI-TOF (ATT matrix, negativemode): 271 [M+2 H]²⁻, 542 [M+2 H]⁻.

5.2 Synthesis of Dendrimeric Azide-functionalized Click Reactionspartners

A detailed reaction scheme for the synthesis of azide-functionalizeddendrimers containing a plurality of hemiacetal groups (protectedaldehyde groups) is shown in FIG. 11.

General Procedure for the Cu(I)-catalysed Triazole Ligation Reaction

To a solution of 9 (7.31 g, 0.0256 mol.), 10 (3.00 g, 0.0128 mol.) inTHF:H₂O (3:1, 40 mL) was added a solution of CuSO₄ (0.103 g, 0.641mmol.) in H₂O (3 mL) followed by solid sodium ascorbate (0.253 g, 1.28mmol.). The reaction mixture was stirred overnight at room temperature.The suspension was diluted with H₂O (50 mL), cooled to 0° C. and treatedwith concentrated NH₄OH (5 mL) for 10 minutes. The reaction mixture wasdiluted with dichloromethane (500 mL) and the organic layer washed withbrine (2×50 mL), followed by H₂O (2×50 mL). The organic layer wasretained, dried (MgSO₄) and concentrated in vacuo. Column chromatography(flash silica) eluting with 1:1 ethyl acetate:petroleum spirit afforded9 (2.76 g), mono-Click product (11, 3.94 g) as a colourless foam,followed by 12 (4.92 g, 48%). The mono-click product (11) was thenreacted with one equivalent of 9 to afford 12 quantitatively afterworkup and with no further purification required. ¹H NMR (CDCl₃, 600MHz): δ 1.29 (s, 6 H, C—CH₃), 1.35 (s, 6 H, C—CH₃), 1.38 (s, 6 H,C—CH₃), 1.49 (s, 6 H, C—CH₃), 4.19 (m, 4H, H4′/H5′), 4.32 (dd, 2H,J=4.8, 2.4 Hz, H 2′), 4.46 (dd, 2H, J=14.4, 8.4 Hz, H6″), 4.50 (s, 2H,—CH₂—), 4.62 (m, 2H, H 3′), 4.64 (m, 2H, H 6′), 5.18 (s, 4H, —CH₂—),5.51 (d, 2H, J=4.8 Hz, H1′), 6.59 (t, 1H, J=1.8 Hz, Ar—H), 6.64 (d, 2H,J=1.8 Hz, Ar—H), 7.79 (s, 2H, C═CH—). ¹³C NMR (CDCl₃, 150.8 Mhz): δ 24.4(C—CH₃), 24.7 (C—CH₃), 25.9 (C—CH₃), 26.0 (C—CH₃), 46.1 (CH₂—), 50.6(—CH6′/H6″), 62.2 (Ar—CH₂—), 67.0 (CH4′), 70.1 (CH2′), 70.5 (CH3′), 70.9(CH5′), 96.0 (CH1′), 102.0 (Ar—CH), 107.9, 109.1, 110.0, 124.0 (C═CH),139.6, 143.4, 160.0. ESI-MS m/z 806 [M+H]⁺.

The reaction of 13 (1.53 g, 1.88 mmol.) and 10 (0.220 g, 0.94 mmol.) inthe presence of CuSO₄ (0.008 g, 0.047 mmol.) and sodium ascorbate (0.019g, 0.094 mmol.) afforded 14 (1.65 g, 95%) as a colourless foam aftercolumn chromatography (flash SiO₂; ethyl acetate:methanol 9:1). ¹H NMR(CDCl₃, 600 MHz): δ 1.26 (s, 12 H, C—CH₃), 1.27 (s, 6 H, C—CH₃), 1.34(s, 12 H, C—CH₃), 1.35 (s, 12 H, C—CH₃), 1.48 (s, 6 H, C—CH₃), 4.19 (m,8H, H4′/H5′), 4.32 (m, 4H, H 2′), 4.46 (m, 4H, H6″), 4.47 (s, 2H,—CH₂—), 4.62 (m, 4H, H 3′), 4.64 (m, 4H, H 6′), 5.12 (s, 8H, —CH₂—),5.15 (s, 4H, —CH₂—), 5.40 (s, 4H, —CH₂—), 5.49 (bd, 4H, J=4.8 Hz, H1′),6.50 (m, 4H, Ar—H), 6.55 (m, 2H, Ar—H), 6.58 (m, 1H, Ar—H), 6.61 (m, 2H,Ar—H), 7.59 (s, 2H, C═CH—), 7.78 (s, 4H, C═CH—). ¹³C NMR (CDCl₃, 150.8MHz): δ 24.4 (C—CH₃), 24.9 (C—CH₃), 25.9 (C—CH₃), 26.0 (C—CH₃), 45.9(CH₂—), 50.4 (—CH6′/H6″), 53.9 (Ar—CH₂—), 61.8 (Ar—CH₂—), 61.9(Ar—CH₂—), 67.0 (CH4′), 70.1 (CH2′), 70.5 (CH3′), 71.1 (CH5′), 96.1(CH1′), 101.6, 101.7, 107.2, 108.0, 109.0, 109.9, 122.9, 124.2, 136.7,140.0, 143.2, 144.1, 159.5, 160.0. MALDI-TOF (ATT, positive mode): m/z1859 [M+H]⁺.

General Procedure for the Conversion of Dendritic Chlorides to Azides

To a solution of 12 (4.84 g, 6.01 mmol.) in acetone:water (4:1, 100 mL)was added NaN₃ (0.586 g, 9.01 mmol.) and heated to reflux under anitrogen atmosphere for 3 hours. The reaction mixture was diluted withethyl acetate (600 mL) and the organic layer washed with brine (2×50 mL)followed by water (2×50 mL). The organic layer was retained, dried(MgSO₄) and concentrated in vacuo to yield 13 (4.72 g, 97%) as a whiteamorphous solid.

¹H NMR (d₆-acetone, 400 MHz): δ 1.28 (s, 6 H, C—CH₃), 1.35 (s, 6 H,C—CH₃), 1.36 (s, 6 H, C—CH₃), 1.44 (s, 6 H, C—CH₃), 4.30 (dd, 2H, J=3.6,2.0 Hz, H 6′/6″), 4.32 (dd, 2H, J=3.2, 1.6 Hz, H 5′), 4.36 (dd, 2H,J=7.6, 1.6 Hz, H 4′), 4.39 (dd, 2H, J=4.8, 2.4 Hz, H 2′), 4.61 (d, 2H,J=3.6 Hz, H 676″), 4.64 (s, 2H, —CH₂), 4.70 (dd, 2H, J=7.6, 2.4 Hz, H3′), 5.20 (s, 4H, —CH₂—), 5.47 (d, 2H, J=4.8 Hz, H1′), 6.73 (m, 3 H,Ar—H), 8.07 (s, 2H, C═C—H). ¹³C NMR (d₆-acetone, 150.8 MHz): δ 25.7(C—CH₃), 26.1 (C—CH₃), 27.2 (C—CH₃), 27.4 (C—CH₃), 47.6 (CH₂—), 52.0(—CH6′/H6″), 63.4 (Ar—CH₂—), 68.8 (CH4′), 72.0 (CH2′), 72.5 (CH3′), 72.9(CH5′), 98.2 (CH1′), 103.3 (Ar—CH), 109.9 (Ar—CH), 110.4, 111.2, 126.3(C═CH), 141.9, 144.8, 161.8. HRMS (ESI, +ve) calcd for C₃₇H₄₉N₉O₁₂Na834.3398 [M+Na]⁺ found 834.3404.

The reaction of 14 (1.51 g, 0.81 mmol.) and NaN₃ (0.079 g, 1.22 mmol.)afforded 15 (1.45 g, 96%) as a white amorphous solid. ¹H NMR (CDCl₃, 600MHz): δ1.27 (s, 12 H, C—CH₃), 1.34 (s, 12 H, C—CH₃), 1.37 (s, 12 H,C—CH₃), 1.48 (s, 12 H, C—CH₃), 4.19 (m, 8H, H4′/H5′), 4.24 (s, 2H,—CH₂—), 4.32 (m, 4 H, H 2), 4.46 (dd, 4H, J=13.8, 8.4 Hz, H6″), 4.62 (m,4H, H 3′), 4.64 (m, 4H, H 6′), 5.12 (s, 4H, —CH₂—), 5.18 (s, 8H, —CH₂—),5.43 (s, 4H, —CH₂—), 5.49 (bd, 4H, J=4.8 Hz, H1′), 6.50 (m, 2H, Ar—H),6.55 (m, 4H, Ar—H), 6.58 (m, 1H, Ar—H), 6.60 (m, 2H, Ar—H), 7.78 (s, 2H,C═CH—), 7.79 (s, 4H, C═CH—). ¹³C NMR (CDCl₃, 150.8 MHz): δ 24.4 (C—CH₃),24.8 (C—CH₃), 25.8 (C—CH₃), 25.9 (C—CH₃), 45.9 (CH₂—), 50.4 (—CH6′/H6″),54.6 (Ar—CH₂—), 62.0 (Ar—CH₂—), 62.1 (Ar—CHr), 67.1 (CH4′), 70.3 (CH2′),70.7 (CH3′), 71.1 (CH5′), 96.2 (CH1′), 101.7, 101.8, 107.4, 107.7,109.0, 109.9, 124.0, 124.2, 137.8, 143.1, 143.4, 144.1, 159.7, 159.9.HRMS (ESI, +ve) calcd for C₈₇H₁₁₀N₂₁O₂₆Na 1886.7829 [M+Na+H]⁺ found1887.7862.

General Procedure for the Dendritic Isopropylidene Deprotection

To a mixture of TFA:water (1:1; 10 mL) was added 13 (0.020 g, 24.7μmol.) under a nitrogen atmosphere. The reaction mixture was heated to50° C. for 4 hours followed by concentration in vacuo. Water (20 mL) wasadded to the mixture and the aqueous layer was washed several times withDCM (3×20 mL), retained and lyophilized overnight to afford 16 (0.015 g,63%) as a pale yellow foam. MALDI-TOF (ATT, positive mode): m/z 652[M+H]⁺.

The reaction of 15 (1.40 g, 0.75 mmol.) with TFA:water (1:1; 20 mL)afforded 17 (1.05 g, 90%) as a pale yellow amorphous solid. MALDI-TOF(ATT, positive mode): m/z 1545 [M+H]⁺.

Example 6 Incorporating of Azide- and Alkyne-modified Nucleosides andNucleotides into Nucleic Acids

Azide- and alkyne modified nucleosides and nucleotides are efficientlyincorporated into nucleic acids by chemical or enzymatic synthesissubstantially as described in Example 2. The resulting modified nucleicacids can be specifically labelled according to the desired applicatione.g. by fluorescent labelling or metal deposition.

This labelling strategy is a fast and represents extremely sensitivemethod for the detection of nucleic acids, nucleic acid sequences andgenes even without the need for PCR amplification.

In a first experiment, to investigate the performance of the Clickreaction within a DNA architecture, the nucleosides 1 and 2 (FIGS. 9 aand b) were prepared and incorporated into oligonucleotides via standardsolid phase synthetic protocols. The efficiency of the Click reactionwas investigated using benzyl azide, CuSO₄, reductant (ascorbate orTCEP) and a copper(I) stabilising ligand. The results of these aresummarised in Table 2. Oligonucleotides comprising the rigid base 1consistently afforded lower yields of the Click product compared withthe flexible alkyne 2. Temperature (10 to 40° C.) did not affect yieldsof the Click reactions.

The efficiency of the Click reaction was then assayed as a function ofazide type exhibiting suitable properties for detection (FIG. 12).Fluorescein azides are extremely sensitive fluorescent markers(fluorescent quantum yield almost unity), whereas the coumarin azideprovides a proof of Click marker as fluorescence is switched on upontriazole formation [19].

TABLE 2 Summary of Click reactions using benzyl azide, CUSO₄ and TCEP.ODN sequences are disclosed as SEQ ID NOS: 11-14, respectively,in order of appearance. X = 1 X = 2 Yield (%) Starting Desired OtherStarting Desired Other ODN sequence Material Product Products MaterialProduct Products 3′-GCG CTT ACX TGT CGC G-5′ 3 97 — — 100 Azidereduction 3′-GCG CTT ACX XGT CGC G-5′ 84 16 — 100 Azide (monoclick)reduction 3′-GCG CTT ACX TGX CGC G-5′ 94  6 — 100 Azide (monoclick)reduction 3′-GCG CTX ACX TGX CGC G-5′ 84 16 NA NA NA (bisclick)

Consistent with the experiments involving the use of benzyl azide,oligodeoxy-nucleotides comprising the rigid alkyne afforded lower Clickconversion yields. The flexible alkyne-containing oligonucleotidesprovided in contrast almost quantitative conversion according to HPLCand MALDI-TOF. Labelling of DNA was again possible directly on the gel.The DNA containing the modified nucleobase was separated from other DNAstrands by gel electrophoresis and the gel was then treated with thefluorescein azide and Cu(I) to perform the Click. Washing of the gelremoved excess fluorescein leaving behind the stained DNA in the gel(FIG. 13).

From these experiments is can be clearly deduced that DNA containing thealkyne modified bases can be selective labelled with fluorescein. CYBRgreen dyes DNA unspecifically and therefore marks also unmodified DNAprior to the click reaction as in lane 1 of A2 and lane 3 of B2 (FIG.13).

Fluorescein is a molecule which fluoresces strongly both as a monomerand after clicking to DNA. After the click reaction with fluorescein,the gel has therefore to be washed in order to remove excess fluoresceinwhich leaved behind the stained DNA.

Coumarin is an alternative fluorescing molecule, which is however notfluorescing as a monomer. It starts to emit fluorescence only after theClick reaction, when the azide is converted into the triazole. Thefluorescence of the coumarin switches effectively on after the click asseen in the below experiment in reaction tubes (FIG. 14). A similarexperiment can be made on the gel.

In a further experiment, the efficiency of the Click reaction wasinvestigated with oligodeoxynucleotides (ODN) incorporating thenucleoside 2 (FIG. 15). This nucleoside was incorporated intooligonucleotides via standard solid phase synthetic protocols using thecorresponding phosphoramidite 1 (FIG. 15). The oligonucleotidescomprising a single or multiple alkyne reporter groups are shown inTable 3.

TABLE 3 ODN sequences are disclosed as SEQ ID NOS:15-17, respectively, in order of appearance. X = 19  ∘Mass StartingODN Sequences Material Product 3′-GCG CTT ACX TGT CGC G-5′ ODN1 ODN1-P4952  5157 (calc) (calc) 4955  5157 (obs) (obs)3′-GCG CTT ACX XGT CGC G-5′ ODN2 ODN2-P 5042  5452 (calc) (calc) 5042 5455 (obs) (obs) 3′-GCG CTT XXX XXX CGC G-5′ ODN6 ODN6-P 5407 6637 (calc) (calc) 5413  6646 (obs) (obs)

The Click procedure involved the sequential addition of azide 3 (FIG.15) (DMSO solution, 10 mM, 50 equiv.), CuSO₄/ligand[29] complex (DMSOsolution, 0.05 M, 20 equiv.) and TCEP (aqueous solution, 0.1 M, 40equiv.) solutions to a 0.2 mM solution of the corresponding ODN. Thereaction mixture was shaken at room temperature overnight. The sampleswere then desalted by membrane and their mass determined by MALDI-TOF(HPA matrix).

Example 7 PCR Amplification of DNA Templates with Modified dNTPs

7.1 PCR Amplification of pol η from Yeast

Template and primers employed for PCR experiments:

Forward primer (SEQ ID NO: 18) 5′-GATTTGGGCCGGATTTGTTTC Reverse primer(SEQ ID NO: 19) 3′-TTTTATGCTATCTCTGATACCCTTG Template:sequence of 318 bp (nt483-800 of Rad30)  of yeast: (SEQ ID NO: 20)GGGCCGGATTTGTTTCAATATGCTAATGTTTGATAATGAGTACGAGCTTACAGGCGACTTGAAACTGAAAGATGCATTAAGCAATATTCGTGAGGCTTTTATAGGGGGCAACTATGATATAAATTCCCATCTACCTCTTATACCCGAAAAGATAAAGTCTCTGAAGTTTGAAGGCGATGTTTTCAATCCAGAGGGCAGAGATCTGATCACAGATTGGGACGATGTAATACTTGCACTAGGATCTCAGGTATGCAAGGGTATCAGAGATAGCATAAAAGATATTCTCGGTTATACTACTTCGTGTGGTTTGTCTAGCAC

The 318 by template contains 59.75% [A+T] and 40.25% [C+G].

A series of commercially available thermostabile polymerases wereassessed for the ability to incorporate the modified deoxyuridinetriphosphates 2 and 8 (FIG. 10) using the PCR reaction. DNA polymerasesused were:

-   -   Pwo and Taq (exo) DNA polymerase (Roche)    -   Vent, Vent (exo), therminator polymerase (from New England        Biolabs)    -   Taq (promega).

A typical PCR reaction contained 0.05 μg genomic S. cerevisiae YPH 499or 0.5 μg DNA template (pDestl7-Poleta yeast[1-1889]), 0.3 mM each ofthe forward and reverse primers, 1.25 U polymerase and 10× polymerasebuffer with magnesium, 200 μM of each unmodified dNTPs (dATP, dCTP anddGTP; NEB) and 200 μM modified dUTP. For the control were naturaltriphosphates (dATP, dCTP, dGTP and dTTP) used. The reactions were donein an overall volume of 50 μL. PCR experiments were performed on anEppendorf Mastercycler Personal.

For amplification hotstart (2 min at 94° C.) was used, followed by 10cycles of amplification (15 sec at 94° C., 30 sec at 53° C., 45 sec at72° C.), 25 cycles (15 sec at 94° C., 30 sec at 56° C., 45 sec at 72°C.) and a final incubation for 2 min at 72° C. PCR products wereanalyzed on a 2% agarose gel by staining with ethidium bromide (FIG.16). PCR products were purified on a QIAquick PCR purification kit(Qiagen), and used for silver staining, sequencing or digestion. Theproducts of PCR reaction were separated by 2% agarose gelelectrophoresis containing ethidium bromide. The products were recordedwith a Ultra-Violet Products CCD camera.

7.2 PCR Amplification of polH from Human

A typical PCR reaction contained 0.5 μg DNA template (pDest17-pIHhuman[1-2142], 0.3 mM each of the forward and reverse primers, 1.25 UPwo polymerase and 10× polymerase buffer with magnesium, 200 μM of eachunmodified dNTPs (dATP, dCTP and dGTP; NEB) and 200 μM modified dUTP.For the control were natural triphosphates (dATP, dCTP, dGTP and dTTP)used. The reactions were done in an overall volume of 50 μL. PCRexperiments were performed on an Eppendorf Mastercycler Personal.

For amplification hotstart (2 min at 94° C.) was used, followed by 10cycles of amplification (15 sec at 94° C., 30 sec at 53° C., 210 sec at72° C.), 30 cycles (15 sec at 94° C., 30 sec at 56° C., 210 sec at 72°C.) and a final incubation for 7 min at 72° C. PCR products wereanalyzed on a 1% agarose gel by staining with ethidium bromide. PCRproducts were purified on a QIAquick PCR purification kit (Qiagen), andused for digestion or sequencing.

The products of PCR reaction were separated by 1% agarose gelelectrophoresis containing ethidium bromide. The products were recordedwith a Ultra-Violet Products CCD camera. The results are shown in FIG.17.

For workup 6 μL of 0.1 M HCl was added and the probes centrifuged (6000rpm, 5 min). The digest was analysed, by HPLC (interchim InterchromUptisphere 3 HDO column (150×2.1 mm), Buffer A: 2 mM TEA/HOAc in H₂O;Buffer B: 2 mM TEA/HOAc H₂O:MeCN 1:4;

30 min; 0%

30% B; 30

32 min; 30%

100% B; 32

36 min; 100% B; 36

38 min; 100%

0% B; 38

60 min; 0% B; flow 0.2 mL/min) (FIG. 18). The different peaks wereassigned by co-injection, UV and FT-ICR-HPLC-MS-MS using the sameconditions

7.3 Enzymatic Digestion of PCR Fragments (318 mer) Incorporating anAlkyne-mediated Nucleotide

For the enzymatic digestion the 318 by DNA template containing themodified nucleotide 8 (FIG. 10) (ca. 10 μg in 100 μL water) wasincubated in 10 μL Buffer A (300 mM ammonium acetate, 100 mM CaCl₂, 1 mMZnSO₄, pH 5.7), 22 units Nuclease P1 (Penicilinum citrium) and 0.05 unitCalf Spleen Phosphodiesterase II. The sample was shaken at 37° C. for 3h. The digest was completed by adding 12 μL Buffer B (500 mM Tris-HCl, 1mM EDTA), 10 units Alkaline Phosphatase (CIP) and 0.1 unit Snake venomphosphodiesterase I (Crotalus adamanteus venom). The sample was shakenfor another 3 h at 37° C.

7.4 General Procedure for the Cu(I)-catalysed Triazole Ligation Reactionof Sugar Azides with Modified ds DNA on Polyacrylamide Gels

All click experiments were run on 318 by PCR fragments comprising either2 or 8 (FIG. 10) in place of dTTP. The modified PCR fragments wereseparated on 5% polyacrylamide gels then each gel was placed in a bathcomprising 1:1 MeOH:H₂O (25 mL). A solution of sugar azide (0.1 M, 3 mL)was added to the bath followed by a solution of CuSO₄ (0.1 M, 600 μL andfinally TCEP (0.1 M, 1.2 mL). These solutions were gently shaken at roomtemperature overnight.

7.5 General Procedure for the Silver Staining of Sugar Azides Linked toDouble-stranded DNA

The click solution was decanted and each gel was washed with 1:1 MeOH:H₂O (3×50 mL, 10 min. each wash), followed by H₂O (3×50 mL, 10 min. eachwash). Each gel was then incubated with the Tollens reagent¹ (40 mL) for30 min. After subsequent washing with H₂O (3×50 mL, 10 min. each wash)the gels were developed with a developing solution comprising 100 mLH₂O, citric acid (1%, 250 μL) and formaldehyde (35%, 80-200 μL).Depending on the formaldehyde concentration, the development process canvary from 2 min. to 20 min. ¹ Preparation of the Tollens reagent: To 80mL H₂O was added AgNO₃ (0.5 M, 5 mL), followed by NaOH (3.0 M, 1.0 mL)and finally NH₄OH (1:1 conc. NH₄OH:H₂O, 2.2 mL).

CONCLUSION

The current invention proposed involves a new and modular method for thesite specific labelling of nucleic acids by via the efficientincorporation of modified triphosphates. These modified triphosphatescomprise groups that can be further functionalized, marked or stainedaccording to the needs of the user. It is foreseeable that RNA labellingcould be achieved via these methods as well using RNA polymerases andreverse transcriptase respectively. Therefore an early and efficientdetection of viral genomes within a host could be effected. The reportednovel nucleic acid labelling protocol is simple, efficient, sensitiveand highly-selective.

Example 8 Detection of Nucleic Acids Using Photographic Processes

The black and white photographic process is one of the most sensitivechemical methods known. Photons captured on photographic paper initiatethe formation of small Ag-nuclei which catalyse further silverdeposition during a subsequent development process [22]. This gives riseto signal amplification factors between 10⁵ for Ag⁺ chemical reductionand 10¹¹ for Ag⁺ photochemical reduction that are similar to thatobtained using the PCR.

We have developed a sensitive method that utilizes photosensitizing dyestethered to nucleic acids, which enables one to potentially detect aparticular gene at subfemtomolar sensitivity (FIG. 21). This new methodis simple (can use conventional photographic materials), fast (detectionin minutes), efficient (only one photosensitising molecule is requiredper biomolecule) and sensitive (current unoptimised sensitivity levelsare ˜10⁻¹⁴-10⁻¹⁵ mol). Coupling this methodology with gene specificbiochemical tools such as primer extension and PCR technologies providesa new and powerful method for the detection of nucleic acids and otheranalytes.

A number of fluorescent cyanine indoline (1 and 2) and quinoline dyederivatives (3) were investigated for their ability to act asphotosensitizers in a photographic process (FIG. 22). The visibleabsorption maxima for 1-3 are 546 nm, 646 nm and 607 nm, respectively.

The indoline dye (1) was readily detected down to the 3×10⁻¹⁴ mol. (30fmol), whereas the limit of detection of (2) was approximately 1-3 fmol(FIGS. 22 a and 22 b). The detection of the quinoline cyanine dye (3)was found to be more sensitive (detection limit ˜0.3 fmol) than theindoline dyes (FIG. 22 c). Background fog may occur upon irradiationwith intense light, however, fog can be suppressed by using a lowintensity infrared light source, although sensitivity is somewhat lower(FIG. 22 d-f).

Control experiments (FIG. 23) using unmodified oligodeoxyribonucleotides(ODN-1, ODN-2, ODN-3) produced a small background negative photographicresponse upon high-energy irradiation at levels of 50 nmol. (i.e. threeorders of magnitude difference). The negative background levels can besuppressed completely if irradiation is conducted with an infrared lampfor 5 minutes (FIG. 23 b). In summary, unmodified DNA gives no staining.

A dilution series of commercially available dyes Cy5 (λ_(max)=646 nm,ODN-4) and Cy5.5 (λ_(max)=646 nm, ODN-5) tethered ODNs were then tested(FIG. 16). The detection limit of ODN-4 was found to be 100 fmol,whereas the sensitivity of Cy5.5 ODN-5 detection was a factor of tenhigher (detection limit 10 fmol). Therefore, although a slight decreasein sensitivity was observed with cyanine dye conjugated ODNs comparedwith their non-tethered controls (FIG. 24), the results clearlydemonstrate that the photography of photosensitizer-conjugatedbiomolecules such as ODNs can be used at a highly sensitive analyticaltool.

Photosensitive dyes, e.g. compounds 4 or 5 also may be introduced intonucleic acids via Click chemistry (FIG. 25).

CONCLUSION

A photographic methodology can be coupled with photosensitizeddye-nucleic acids to create a fast, simple, efficient and sensitivemethod for analyte, e.g. nucleic acid, detection.

Suitable examples of photosensitizer groups are quinoline-based cyaninedyes (e.g. 3) or indoline dyes (e.g. 1 or 2) as shown in FIG. 22, whichoffer sensitives of at least 10 fmol (1), 1 fmol (2) or 0.1 fmol (3).

Indoline-based dyes such as Cy5 and Cy5.5 tethered tooligodeoxyribonucleotides may be detected at levels of 100 fmol and 10fmol, respectively.

LITERATURE

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1. A nucleic acid or a nucleic acid analogue molecule havingincorporated therein at least one compound of formula (II):C—S—N  (II) wherein C is a Click functional group selected from alkyneand azide groups which is a first reaction partner for a Click reaction,said Click reaction being a (3+2) cycloaddition reaction between azideand alkyne groups forming a 1,2,3-triazole ring S is a spacer, and N isa nucleic acid or nucleic acid analogue building block such as anucleosidic or nucleotidic compound, wherein the Click functional groupis attached to a nucleobase, wherein the functional group is an alkynegroup attached to position 5 and/or 6 of a pyrimidine nucleobase, or topositions 7 and/or 8 of a purine nucleobase, and wherein the nucleicacid or nucleic acid analogue molecule is capable of hybridising with acomplementary nucleic acid.
 2. The nucleic acid or a nucleic acidanalogue molecule of claim 1, wherein the compound of formula (II)further comprises marker groups or marker precursor groups.
 3. Thenucleic acid or a nucleic acid analogue molecule of claim 1, wherein thenucleobase is selected from the group consisting of naturally occurringand non-naturally occurring purine and pyrimidine bases.
 4. The nucleicacid or a nucleic acid analogue molecule of claim 1, wherein thenucleobase is selected from the group consisting of adenine,7-deazaguanine, guanine, 7-deazaguanine, cytosine, thymidine, uracil,inosine, and xanthine.
 5. The nucleic acid or a nucleic acid analoguemolecule of claim 1, wherein the functional group is attached topositions 5 and 6 of a pyrimidine nucleobase, or to positions 7 and 8 ofa purine nucleobase.
 6. The nucleic acid or a nucleic acid analoguemolecule of claim 1, wherein the spacer is an at least partially rigidspacer.
 7. The nucleic acid or a nucleic acid analogue molecule of claim1, wherein the spacer comprises at least one group selected from thegroup consisting of alkene groups, alkyne groups, cyclic groups,aromatic groups, heteroaromatic groups, and combinations thereof.
 8. Thenucleic acid or a nucleic acid analogue molecule of claim 1, wherein themolecule is a building block for the chemical or enzymatic synthesis ofnucleic acids or nucleic acid analogues or a precursor thereof.
 9. Thenucleic acid or a nucleic acid analogue molecule of claim 1, wherein themolecule is a nucleoside triphosphate, a ribose, 2′-deoxyribose, a2′,3′-dideoxyribose nucleoside triphosphate, a nucleosidephosphoramidite, H-phosphonate or phosphotriester.
 10. The nucleic acidor a nucleic acid analogue molecule of claim 1, wherein the molecule isa building block for the synthesis of peptide nucleic acids, morpholinonucleic acids, or locked nucleic acids.
 11. The nucleic acid or anucleic acid analogue molecule of claim 1, wherein the functional groupis attached to the nucleobase via a spacer having a chain length of upto 10 atoms.
 12. The nucleic acid or a nucleic acid analogue molecule ofclaims 1, wherein the chain length is of up to 3 atoms.
 13. The nucleicacid or a nucleic acid analogue molecule of claim 1 which is a nucleicacid selected from the group consisting of DNA and RNA, or a nucleicacid analogue molecule selected from the group consisting of peptidicnucleic acids, morpholino nucleic acids and locked nucleic acids.
 14. Anassociation product of the nucleic acid or nucleic acid analoguemolecule of claim 1 with an analyte.
 15. An association product of thenucleic acid or nucleic acid analogue molecule of claim 13 with ananalyte.
 16. The product of claim 14 which is a hybridization productwith a complementary nucleic acid.
 17. The product of claim 15 which isa hybridization product with a complementary nucleic acid.
 18. Acompound obtained by synthesizing a nucleic acid or nucleic acidanalogue molecule that is capable of hybridizing with a complementarynucleic acid, comprising incorporating a nucleotide or nucleotideanalogue building block comprising a compound (II):C—S—N  (II) wherein C is a Click functional group selected from alkyneand azide groups which is a first reaction partner for a Click reaction,said Click reaction being a (3+2) cycloaddition reaction between azideand alkyne groups forming a 1,2,3-triazole ring, S is a spacer, and N isa nucleic acid or nucleic acid analogue building block such as anucleosidic or nucleotidic compound, wherein the Click functional groupis attached to a nucleobase; and contacting the nucleic acid or nucleicacid analogue molecule with a second reaction partner of compound (II)and performing a Click reaction between the first and second reactionpartners, said Click reaction being a (3+2) cycloaddition reactionbetween azide and alkyne groups forming a 1,2,3-triazole ring, whereinthe functional group is an alkyne group attached to positions 5 or/and 6of a pyrimidine nucleobase, or to positions 7 or/and 8 of a purinenucleobase into a nucleic acid or nucleic acid analogue molecule.
 19. Anassociation product of the compound of claim 18 with a complementarynucleic acid.